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‎README.md‎

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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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| 0566 |[Reshape the Matrix](src/main/kotlin/g0501_0600/s0566_reshape_the_matrix)| Easy | Array, Matrix, Simulation | 239 | 99.05
6061

6162
#### Day 8 String
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@@ -154,6 +155,7 @@
154155
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
155156
|-|-|-|-|-|-
156157
| 0503 |[Next Greater Element II](src/main/kotlin/g0501_0600/s0503_next_greater_element_ii)| Medium | Array, Stack, Monotonic_Stack | 331 | 92.68
158+
| 0556 |[Next Greater Element III](src/main/kotlin/g0501_0600/s0556_next_greater_element_iii)| Medium | String, Math, Two_Pointers | 137 | 80.00
157159

158160
#### Day 11
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@@ -245,6 +247,7 @@
245247

246248
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
247249
|-|-|-|-|-|-
250+
| 0542 |[01 Matrix](src/main/kotlin/g0501_0600/s0542_01_matrix)| Medium | Array, Dynamic_Programming, Breadth_First_Search, Matrix | 441 | 94.06
248251

249252
#### Day 6 Matrix Related Problems
250253

@@ -260,6 +263,7 @@
260263

261264
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
262265
|-|-|-|-|-|-
266+
| 0547 |[Number of Provinces](src/main/kotlin/g0501_0600/s0547_number_of_provinces)| Medium | Depth_First_Search, Breadth_First_Search, Graph, Union_Find | 229 | 79.73
263267

264268
#### Day 9 Standard Traversal
265269

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300304

301305
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
302306
|-|-|-|-|-|-
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| 0584 |[Find Customer Referee](src/main/kotlin/g0501_0600/s0584_find_customer_referee)| Easy | Database | 779 | 43.48
303308
| 0183 |[Customers Who Never Order](src/main/kotlin/g0101_0200/s0183_customers_who_never_order)| Easy | Database | 712 | 33.67
304309

305310
#### Day 2 Select and Order
@@ -340,6 +345,7 @@
340345

341346
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0586 |[Customer Placing the Largest Number of Orders](src/main/kotlin/g0501_0600/s0586_customer_placing_the_largest_number_of_orders)| Easy | LeetCode_Curated_SQL_70, Database | 768 | 44.85
343349
| 0511 |[Game Play Analysis I](src/main/kotlin/g0501_0600/s0511_game_play_analysis_i)| Easy | LeetCode_Curated_SQL_70, Database | 790 | 45.04
344350

345351
#### Day 9 Control of Flow
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583589
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
584590
|-|-|-|-|-|-
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| 0547 |[Number of Provinces](src/main/kotlin/g0501_0600/s0547_number_of_provinces)| Medium | Depth_First_Search, Breadth_First_Search, Graph, Union_Find | 229 | 79.73
585592

586593
#### Day 20 Brute Force/Backtracking
587594

@@ -645,6 +652,7 @@
645652
| 0448 |[Find All Numbers Disappeared in an Array](src/main/kotlin/g0401_0500/s0448_find_all_numbers_disappeared_in_an_array)| Easy | Array, Hash_Table | 394 | 100.00
646653
| 0442 |[Find All Duplicates in an Array](src/main/kotlin/g0401_0500/s0442_find_all_duplicates_in_an_array)| Medium | Array, Hash_Table | 480 | 73.81
647654
| 0041 |[First Missing Positive](src/main/kotlin/g0001_0100/s0041_first_missing_positive)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table | 345 | 100.00
655+
| 0532 |[K-diff Pairs in an Array](src/main/kotlin/g0501_0600/s0532_k_diff_pairs_in_an_array)| Medium | Array, Hash_Table, Sorting, Binary_Search, Two_Pointers | 230 | 84.62
648656
| 0456 |[132 Pattern](src/main/kotlin/g0401_0500/s0456_132_pattern)| Medium | Array, Binary_Search, Stack, Ordered_Set, Monotonic_Stack | 434 | 100.00
649657
| 0239 |[Sliding Window Maximum](src/main/kotlin/g0201_0300/s0239_sliding_window_maximum)| Hard | Top_100_Liked_Questions, Top_Interview_Questions, Array, Heap_Priority_Queue, Sliding_Window, Queue, Monotonic_Queue | 1059 | 86.14
650658

@@ -812,6 +820,7 @@
812820

813821
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
814822
|-|-|-|-|-|-
823+
| 0566 |[Reshape the Matrix](src/main/kotlin/g0501_0600/s0566_reshape_the_matrix)| Easy | Array, Matrix, Simulation | 239 | 99.05
815824
| 0118 |[Pascal's Triangle](src/main/kotlin/g0101_0200/s0118_pascals_triangle)| Easy | Top_Interview_Questions, Array, Dynamic_Programming | 277 | 33.22
816825

817826
#### Day 5 Array
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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
10631072
|-|-|-|-|-|-
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| 0344 |[Reverse String](src/main/kotlin/g0301_0400/s0344_reverse_string)| Easy | Top_Interview_Questions, String, Two_Pointers, Recursion | 445 | 69.75
1074+
| 0557 |[Reverse Words in a String III](src/main/kotlin/g0501_0600/s0557_reverse_words_in_a_string_iii)| Easy | String, Two_Pointers | 215 | 98.10
10651075

10661076
#### Day 5 Two Pointers
10671077

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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
10751085
|-|-|-|-|-|-
10761086
| 0003 |[Longest Substring Without Repeating Characters](src/main/kotlin/g0001_0100/s0003_longest_substring_without_repeating_characters)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Hash_Table, Sliding_Window | 258 | 91.09
1087+
| 0567 |[Permutation in String](src/main/kotlin/g0501_0600/s0567_permutation_in_string)| Medium | String, Hash_Table, Two_Pointers, Sliding_Window | 169 | 100.00
10771088

10781089
#### Day 7 Breadth First Search Depth First Search
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10901101

10911102
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
10921103
|-|-|-|-|-|-
1104+
| 0542 |[01 Matrix](src/main/kotlin/g0501_0600/s0542_01_matrix)| Medium | Array, Dynamic_Programming, Breadth_First_Search, Matrix | 441 | 94.06
10931105
| 0994 |[Rotting Oranges](src/main/kotlin/g0901_1000/s0994_rotting_oranges)| Medium | Array, Breadth_First_Search, Matrix | 308 | 57.93
10941106

10951107
#### Day 10 Recursion Backtracking
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11701182
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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11721184
| 0200 |[Number of Islands](src/main/kotlin/g0101_0200/s0200_number_of_islands)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Depth_First_Search, Breadth_First_Search, Matrix, Union_Find | 252 | 95.41
1185+
| 0547 |[Number of Provinces](src/main/kotlin/g0501_0600/s0547_number_of_provinces)| Medium | Depth_First_Search, Breadth_First_Search, Graph, Union_Find | 229 | 79.73
11731186

11741187
#### Day 7 Breadth First Search Depth First Search
11751188

11761189
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
11771190
|-|-|-|-|-|-
11781191
| 0117 |[Populating Next Right Pointers in Each Node II](src/main/kotlin/g0101_0200/s0117_populating_next_right_pointers_in_each_node_ii)| Medium | Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Linked_List | 199 | 94.67
1192+
| 0572 |[Subtree of Another Tree](src/main/kotlin/g0501_0600/s0572_subtree_of_another_tree)| Easy | Depth_First_Search, Tree, Binary_Tree, Hash_Function, String_Matching | 214 | 92.39
11791193

11801194
#### Day 8 Breadth First Search Depth First Search
11811195

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12451259
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
12461260
|-|-|-|-|-|-
12471261
| 1143 |[Longest Common Subsequence](src/main/kotlin/g1101_1200/s1143_longest_common_subsequence)| Medium | Top_100_Liked_Questions, String, Dynamic_Programming | 307 | 38.36
1262+
| 0583 |[Delete Operation for Two Strings](src/main/kotlin/g0501_0600/s0583_delete_operation_for_two_strings)| Medium | String, Dynamic_Programming | 197 | 100.00
12481263

12491264
#### Day 18 Dynamic Programming
12501265

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13981413

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| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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|-|-|-|-|-|-
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| 0540 |[Single Element in a Sorted Array](src/main/kotlin/g0501_0600/s0540_single_element_in_a_sorted_array)| Medium | Array, Binary_Search | 274 | 86.67
14011417

14021418
#### Day 10
14031419

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14231439
| <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
14241440
|-|-|-|-|-|-
14251441
| 0154 |[Find Minimum in Rotated Sorted Array II](src/main/kotlin/g0101_0200/s0154_find_minimum_in_rotated_sorted_array_ii)| Hard | Array, Binary_Search | 275 | 84.00
1442+
| 0528 |[Random Pick with Weight](src/main/kotlin/g0501_0600/s0528_random_pick_with_weight)| Medium | Math, Binary_Search, Prefix_Sum, Randomized | 393 | 91.38
14261443

14271444
#### Day 14
14281445

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16131630
| 0763 |[Partition Labels](src/main/kotlin/g0701_0800/s0763_partition_labels)| Medium | Top_100_Liked_Questions, String, Hash_Table, Greedy, Two_Pointers, Data_Structure_II_Day_7_String | 235 | 84.75
16141631
| 0739 |[Daily Temperatures](src/main/kotlin/g0701_0800/s0739_daily_temperatures)| Medium | Top_100_Liked_Questions, Array, Stack, Monotonic_Stack, Programming_Skills_II_Day_6 | 936 | 80.54
16151632
| 0647 |[Palindromic Substrings](src/main/kotlin/g0601_0700/s0647_palindromic_substrings)| Medium | Top_100_Liked_Questions, String, Dynamic_Programming | 266 | 67.83
1633+
| 0587 |[Erect the Fence](src/main/kotlin/g0501_0600/s0587_erect_the_fence)| Hard | Array, Math, Geometry | 470 | 100.00
1634+
| 0586 |[Customer Placing the Largest Number of Orders](src/main/kotlin/g0501_0600/s0586_customer_placing_the_largest_number_of_orders)| Easy | LeetCode_Curated_SQL_70, Database, SQL_I_Day_8_Function | 768 | 44.85
1635+
| 0584 |[Find Customer Referee](src/main/kotlin/g0501_0600/s0584_find_customer_referee)| Easy | Database, SQL_I_Day_1_Select | 779 | 43.48
1636+
| 0583 |[Delete Operation for Two Strings](src/main/kotlin/g0501_0600/s0583_delete_operation_for_two_strings)| Medium | String, Dynamic_Programming, Algorithm_II_Day_17_Dynamic_Programming | 197 | 100.00
1637+
| 0581 |[Shortest Unsorted Continuous Subarray](src/main/kotlin/g0501_0600/s0581_shortest_unsorted_continuous_subarray)| Medium | Array, Sorting, Greedy, Two_Pointers, Stack, Monotonic_Stack | 246 | 100.00
1638+
| 0576 |[Out of Boundary Paths](src/main/kotlin/g0501_0600/s0576_out_of_boundary_paths)| Medium | Dynamic_Programming | 153 | 100.00
1639+
| 0575 |[Distribute Candies](src/main/kotlin/g0501_0600/s0575_distribute_candies)| Easy | Array, Hash_Table | 538 | 76.92
1640+
| 0572 |[Subtree of Another Tree](src/main/kotlin/g0501_0600/s0572_subtree_of_another_tree)| Easy | Depth_First_Search, Tree, Binary_Tree, Hash_Function, String_Matching, Algorithm_II_Day_7_Breadth_First_Search_Depth_First_Search | 214 | 92.39
1641+
| 0567 |[Permutation in String](src/main/kotlin/g0501_0600/s0567_permutation_in_string)| Medium | String, Hash_Table, Two_Pointers, Sliding_Window, Algorithm_I_Day_6_Sliding_Window | 169 | 100.00
1642+
| 0566 |[Reshape the Matrix](src/main/kotlin/g0501_0600/s0566_reshape_the_matrix)| Easy | Array, Matrix, Simulation, Data_Structure_I_Day_4_Array, Programming_Skills_I_Day_7_Array | 239 | 99.05
1643+
| 0565 |[Array Nesting](src/main/kotlin/g0501_0600/s0565_array_nesting)| Medium | Array, Depth_First_Search | 553 | 100.00
1644+
| 0564 |[Find the Closest Palindrome](src/main/kotlin/g0501_0600/s0564_find_the_closest_palindrome)| Hard | String, Math | 179 | 100.00
1645+
| 0563 |[Binary Tree Tilt](src/main/kotlin/g0501_0600/s0563_binary_tree_tilt)| Easy | Depth_First_Search, Tree, Binary_Tree | 197 | 100.00
1646+
| 0561 |[Array Partition](src/main/kotlin/g0501_0600/s0561_array_partition_i)| Easy | Array, Sorting, Greedy, Counting_Sort | 337 | 90.48
16161647
| 0560 |[Subarray Sum Equals K](src/main/kotlin/g0501_0600/s0560_subarray_sum_equals_k)| Medium | Top_100_Liked_Questions, Array, Hash_Table, Prefix_Sum, Data_Structure_II_Day_5_Array | 692 | 53.27
1648+
| 0559 |[Maximum Depth of N-ary Tree](src/main/kotlin/g0501_0600/s0559_maximum_depth_of_n_ary_tree)| Easy | Depth_First_Search, Breadth_First_Search, Tree | 196 | 100.00
1649+
| 0558 |[Logical OR of Two Binary Grids Represented as Quad-Trees](src/main/kotlin/g0501_0600/s0558_logical_or_of_two_binary_grids_represented_as_quad_trees)| Medium | Tree, Divide_and_Conquer | 268 | 100.00
1650+
| 0557 |[Reverse Words in a String III](src/main/kotlin/g0501_0600/s0557_reverse_words_in_a_string_iii)| Easy | String, Two_Pointers, Algorithm_I_Day_4_Two_Pointers | 215 | 98.10
1651+
| 0556 |[Next Greater Element III](src/main/kotlin/g0501_0600/s0556_next_greater_element_iii)| Medium | String, Math, Two_Pointers, Programming_Skills_II_Day_10 | 137 | 80.00
1652+
| 0554 |[Brick Wall](src/main/kotlin/g0501_0600/s0554_brick_wall)| Medium | Array, Hash_Table | 307 | 100.00
1653+
| 0553 |[Optimal Division](src/main/kotlin/g0501_0600/s0553_optimal_division)| Medium | Array, Dynamic_Programming, Math | 154 | 100.00
1654+
| 0552 |[Student Attendance Record II](src/main/kotlin/g0501_0600/s0552_student_attendance_record_ii)| Hard | Dynamic_Programming | 151 | 100.00
1655+
| 0551 |[Student Attendance Record I](src/main/kotlin/g0501_0600/s0551_student_attendance_record_i)| Easy | String | 151 | 95.00
1656+
| 0547 |[Number of Provinces](src/main/kotlin/g0501_0600/s0547_number_of_provinces)| Medium | Depth_First_Search, Breadth_First_Search, Graph, Union_Find, Algorithm_II_Day_6_Breadth_First_Search_Depth_First_Search, Graph_Theory_I_Day_8_Standard_Traversal, Level_2_Day_19_Union_Find | 229 | 79.73
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| 0546 |[Remove Boxes](src/main/kotlin/g0501_0600/s0546_remove_boxes)| Hard | Array, Dynamic_Programming, Memoization | 283 | 100.00
16171658
| 0543 |[Diameter of Binary Tree](src/main/kotlin/g0501_0600/s0543_diameter_of_binary_tree)| Easy | Top_100_Liked_Questions, Depth_First_Search, Tree, Binary_Tree, Level_2_Day_7_Tree, Udemy_Tree_Stack_Queue | 307 | 43.93
1659+
| 0542 |[01 Matrix](src/main/kotlin/g0501_0600/s0542_01_matrix)| Medium | Array, Dynamic_Programming, Breadth_First_Search, Matrix, Algorithm_I_Day_9_Breadth_First_Search_Depth_First_Search, Graph_Theory_I_Day_5_Matrix_Related_Problems | 441 | 94.06
1660+
| 0541 |[Reverse String II](src/main/kotlin/g0501_0600/s0541_reverse_string_ii)| Easy | String, Two_Pointers | 200 | 83.33
1661+
| 0540 |[Single Element in a Sorted Array](src/main/kotlin/g0501_0600/s0540_single_element_in_a_sorted_array)| Medium | Array, Binary_Search, Binary_Search_II_Day_9 | 274 | 86.67
1662+
| 0539 |[Minimum Time Difference](src/main/kotlin/g0501_0600/s0539_minimum_time_difference)| Medium | Array, String, Math, Sorting | 183 | 100.00
1663+
| 0538 |[Convert BST to Greater Tree](src/main/kotlin/g0501_0600/s0538_convert_bst_to_greater_tree)| Medium | Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree | 252 | 77.78
1664+
| 0537 |[Complex Number Multiplication](src/main/kotlin/g0501_0600/s0537_complex_number_multiplication)| Medium | String, Math, Simulation | 171 | 75.00
1665+
| 0535 |[Encode and Decode TinyURL](src/main/kotlin/g0501_0600/s0535_encode_and_decode_tinyurl)| Medium | String, Hash_Table, Design, Hash_Function | 183 | 81.25
1666+
| 0532 |[K-diff Pairs in an Array](src/main/kotlin/g0501_0600/s0532_k_diff_pairs_in_an_array)| Medium | Array, Hash_Table, Sorting, Binary_Search, Two_Pointers, Udemy_Arrays | 230 | 84.62
1667+
| 0530 |[Minimum Absolute Difference in BST](src/main/kotlin/g0501_0600/s0530_minimum_absolute_difference_in_bst)| Easy | Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Binary_Search_Tree | 209 | 86.96
1668+
| 0529 |[Minesweeper](src/main/kotlin/g0501_0600/s0529_minesweeper)| Medium | Array, Depth_First_Search, Breadth_First_Search, Matrix | 243 | 87.50
1669+
| 0528 |[Random Pick with Weight](src/main/kotlin/g0501_0600/s0528_random_pick_with_weight)| Medium | Math, Binary_Search, Prefix_Sum, Randomized, Binary_Search_II_Day_13 | 393 | 91.38
1670+
| 0526 |[Beautiful Arrangement](src/main/kotlin/g0501_0600/s0526_beautiful_arrangement)| Medium | Array, Dynamic_Programming, Bit_Manipulation, Backtracking, Bitmask | 107 | 100.00
16181671
| 0525 |[Contiguous Array](src/main/kotlin/g0501_0600/s0525_contiguous_array)| Medium | Array, Hash_Table, Prefix_Sum | 471 | 100.00
16191672
| 0524 |[Longest Word in Dictionary through Deleting](src/main/kotlin/g0501_0600/s0524_longest_word_in_dictionary_through_deleting)| Medium | Array, String, Sorting, Two_Pointers | 307 | 100.00
16201673
| 0523 |[Continuous Subarray Sum](src/main/kotlin/g0501_0600/s0523_continuous_subarray_sum)| Medium | Array, Hash_Table, Math, Prefix_Sum | 682 | 95.45

‎src/main/kotlin/g0501_0600/s0526_beautiful_arrangement/readme.md‎

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[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
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[![](https://img.shields.io/github/forks/javadev/LeetCode-in-Kotlin?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin/fork)
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## 526\. Beautiful Arrangement
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Medium
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Suppose you have `n` integers labeled `1` through `n`. A permutation of those `n` integers `perm` (**1-indexed**) is considered a **beautiful arrangement** if for every `i` (`1 <= i <= n`), **either** of the following is true:
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* `perm[i]` is divisible by `i`.
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* `i` is divisible by `perm[i]`.
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Given an integer `n`, return _the **number** of the **beautiful arrangements** that you can construct_.
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**Example 1:**
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**Input:** n = 2
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**Output:** 2
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**Explanation:**
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The first beautiful arrangement is [1,2]:
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- perm[1] = 1 is divisible by i = 1
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- perm[2] = 2 is divisible by i = 2
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The second beautiful arrangement is [2,1]:
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- perm[1] = 2 is divisible by i = 1
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- i = 2 is divisible by perm[2] = 1
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**Example 2:**
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**Input:** n = 1
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**Output:** 1
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**Constraints:**
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* `1 <= n <= 15`
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## Solution
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```kotlin
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class Solution {
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fun countArrangement(n: Int): Int {
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return backtrack(n, n, arrayOfNulls(1 shl n + 1), 0)
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}
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private fun backtrack(n: Int, index: Int, cache: Array<Int?>, cacheindex: Int): Int {
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if (index == 0) {
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return 1
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}
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var result = 0
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if (cache[cacheindex] != null) {
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return cache[cacheindex]!!
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}
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for (i in n downTo 1) {
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if (cacheindex and (1 shl i) == 0 && (i % index == 0 || index % i == 0)) {
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result += backtrack(n, index - 1, cache, cacheindex or (1 shl i))
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}
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}
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cache[cacheindex] = result
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return result
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}
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}
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```

‎src/main/kotlin/g0501_0600/s0528_random_pick_with_weight/readme.md‎

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[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
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[![](https://img.shields.io/github/forks/javadev/LeetCode-in-Kotlin?label=Fork%20me%20on%20GitHub%20&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin/fork)
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## 528\. Random Pick with Weight
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Medium
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You are given a **0-indexed** array of positive integers `w` where `w[i]` describes the **weight** of the <code>i<sup>th</sup></code> index.
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You need to implement the function `pickIndex()`, which **randomly** picks an index in the range `[0, w.length - 1]` (**inclusive**) and returns it. The **probability** of picking an index `i` is `w[i] / sum(w)`.
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* For example, if `w = [1, 3]`, the probability of picking index `0` is `1 / (1 + 3) = 0.25` (i.e., `25%`), and the probability of picking index `1` is `3 / (1 + 3) = 0.75` (i.e., `75%`).
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**Example 1:**
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**Input** ["Solution","pickIndex"] [[[1]],[]]
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**Output:** [null,0]
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**Explanation:**
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Solution solution = new Solution([1]);
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solution.pickIndex(); // return 0. The only option is to return 0 since there is only one element in w.
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**Example 2:**
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**Input**
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["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
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[[[1,3]],[],[],[],[],[]]
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**Output:** [null,1,1,1,1,0]
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**Explanation:**
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Solution solution = new Solution([1, 3]);
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solution.pickIndex(); // return 1. It is returning the second element (index = 1) that has a probability of 3/4.
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 1
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solution.pickIndex(); // return 0. It is returning the first element (index = 0) that has a probability of 1/4.
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Since this is a randomization problem, multiple answers are allowed.
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All of the following outputs can be considered correct:
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[null,1,1,1,1,0]
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[null,1,1,1,1,1]
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[null,1,1,1,0,0]
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[null,1,1,1,0,1]
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[null,1,0,1,0,0]
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......
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and so on.
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**Constraints:**
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* <code>1 <= w.length <= 10<sup>4</sup></code>
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* <code>1 <= w[i] <= 10<sup>5</sup></code>
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* `pickIndex` will be called at most <code>10<sup>4</sup></code> times.
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## Solution
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```kotlin
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import java.util.Random
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import java.util.TreeMap
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@Suppress("kotlin:S2245")
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class Solution(val w: IntArray) {
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var x: IntArray = IntArray(w.size) { 0 }
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val rand = Random()
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val tree = TreeMap<Int, Int>()
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var sum = 0
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init {
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for (i in w.indices) {
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tree.put(sum, i)
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sum += w[i]
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}
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}
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fun pickIndex(): Int {
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val r = rand.nextInt(sum)
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return tree.floorEntry(r).value!!
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}
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}
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/*
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* Your Solution object will be instantiated and called as such:
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* var obj = Solution(w)
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* var param_1 = obj.pickIndex()
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*/
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```

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