Added tasks 171-187.

README.md

@@ -486,6 +486,7 @@
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0061 |[Rotate List](src/main/kotlin/g0001_0100/s0061_rotate_list)| Medium | Two_Pointers, Linked_List | 193 | 92.16
+| 0173 |[Binary Search Tree Iterator](src/main/kotlin/g0101_0200/s0173_binary_search_tree_iterator)| Medium | Tree, Binary_Tree, Stack, Design, Binary_Search_Tree, Iterator | 563 | 46.91
 
 #### Day 17
 
@@ -588,6 +589,7 @@
 
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+| 0183 |[Customers Who Never Order](src/main/kotlin/g0101_0200/s0183_customers_who_never_order)| Easy | Database | 712 | 33.67
 
 #### Day 2 Select and Order
 
@@ -603,11 +605,13 @@
 
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+| 0176 |[Second Highest Salary](src/main/kotlin/g0101_0200/s0176_second_highest_salary)| Medium | Database | 219 | 92.54
 
 #### Day 5 Union
 
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+| 0175 |[Combine Two Tables](src/main/kotlin/g0101_0200/s0175_combine_two_tables)| Easy | Database | 473 | 54.97
 
 #### Day 6 Union
 
@@ -633,6 +637,7 @@
 
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+| 0182 |[Duplicate Emails](src/main/kotlin/g0101_0200/s0182_duplicate_emails)| Easy | Database | 396 | 68.40
 
 ### Level 1
 
@@ -783,6 +788,7 @@
 |-|-|-|-|-|-
 | 0108 |[Convert Sorted Array to Binary Search Tree](src/main/kotlin/g0101_0200/s0108_convert_sorted_array_to_binary_search_tree)| Easy | Top_Interview_Questions, Array, Tree, Binary_Tree, Binary_Search_Tree, Divide_and_Conquer | 334 | 35.39
 | 0230 |[Kth Smallest Element in a BST](src/main/kotlin/g0201_0300/s0230_kth_smallest_element_in_a_bst)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree | 393 | 33.33
+| 0173 |[Binary Search Tree Iterator](src/main/kotlin/g0101_0200/s0173_binary_search_tree_iterator)| Medium | Tree, Binary_Tree, Stack, Design, Binary_Search_Tree, Iterator | 563 | 46.91
 
 #### Day 10 Graph/BFS/DFS
 
@@ -865,13 +871,15 @@
 | 0136 |[Single Number](src/main/kotlin/g0101_0200/s0136_single_number)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Bit_Manipulation | 344 | 83.63
 | 0007 |[Reverse Integer](src/main/kotlin/g0001_0100/s0007_reverse_integer)| Medium | Top_Interview_Questions, Math | 245 | 60.32
 | 0009 |[Palindrome Number](src/main/kotlin/g0001_0100/s0009_palindrome_number)| Easy | Math | 238 | 96.24
+| 0172 |[Factorial Trailing Zeroes](src/main/kotlin/g0101_0200/s0172_factorial_trailing_zeroes)| Medium | Top_Interview_Questions, Math | 220 | 67.65
 | 0050 |[Pow(x, n)](src/main/kotlin/g0001_0100/s0050_powx_n)| Medium | Top_Interview_Questions, Math, Recursion | 264 | 52.98
 
 #### Udemy Strings
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
 |-|-|-|-|-|-
 | 0014 |[Longest Common Prefix](src/main/kotlin/g0001_0100/s0014_longest_common_prefix)| Easy | Top_Interview_Questions, String | 209 | 88.86
+| 0187 |[Repeated DNA Sequences](src/main/kotlin/g0101_0200/s0187_repeated_dna_sequences)| Medium | String, Hash_Table, Bit_Manipulation, Sliding_Window, Hash_Function, Rolling_Hash | 319 | 79.03
 | 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
 | 0020 |[Valid Parentheses](src/main/kotlin/g0001_0100/s0020_valid_parentheses)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, String, Stack | 226 | 72.53
 | 0005 |[Longest Palindromic Substring](src/main/kotlin/g0001_0100/s0005_longest_palindromic_substring)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Dynamic_Programming | 323 | 75.48
@@ -1179,6 +1187,7 @@
 
 | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- --> | <!-- -->
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+| 0187 |[Repeated DNA Sequences](src/main/kotlin/g0101_0200/s0187_repeated_dna_sequences)| Medium | String, Hash_Table, Bit_Manipulation, Sliding_Window, Hash_Function, Rolling_Hash | 319 | 79.03
 | 0005 |[Longest Palindromic Substring](src/main/kotlin/g0001_0100/s0005_longest_palindromic_substring)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, String, Dynamic_Programming | 323 | 75.48
 
 #### Day 10 Linked List
@@ -1234,6 +1243,7 @@
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 |-|-|-|-|-|-
 | 0230 |[Kth Smallest Element in a BST](src/main/kotlin/g0201_0300/s0230_kth_smallest_element_in_a_bst)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Depth_First_Search, Tree, Binary_Tree, Binary_Search_Tree | 393 | 33.33
+| 0173 |[Binary Search Tree Iterator](src/main/kotlin/g0101_0200/s0173_binary_search_tree_iterator)| Medium | Tree, Binary_Tree, Stack, Design, Binary_Search_Tree, Iterator | 563 | 46.91
 
 #### Day 18 Tree
 
@@ -1525,6 +1535,22 @@
 | 0199 |[Binary Tree Right Side View](src/main/kotlin/g0101_0200/s0199_binary_tree_right_side_view)| Medium | Depth_First_Search, Breadth_First_Search, Tree, Binary_Tree, Data_Structure_II_Day_16_Tree, Level_2_Day_15_Tree | 194 | 92.89
 | 0198 |[House Robber](src/main/kotlin/g0101_0200/s0198_house_robber)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Dynamic_Programming, Algorithm_I_Day_12_Dynamic_Programming, Dynamic_Programming_I_Day_3, Level_2_Day_12_Dynamic_Programming, Udemy_Dynamic_Programming | 156 | 92.24
 | 0189 |[Rotate Array](src/main/kotlin/g0101_0200/s0189_rotate_array)| Medium | Top_100_Liked_Questions, Top_Interview_Questions, Array, Math, Two_Pointers, Algorithm_I_Day_2_Two_Pointers, Udemy_Arrays | 483 | 86.95
+| 0187 |[Repeated DNA Sequences](src/main/kotlin/g0101_0200/s0187_repeated_dna_sequences)| Medium | String, Hash_Table, Bit_Manipulation, Sliding_Window, Hash_Function, Rolling_Hash, Data_Structure_II_Day_9_String, Udemy_Strings | 319 | 79.03
+| 0185 |[Department Top Three Salaries](src/main/kotlin/g0101_0200/s0185_department_top_three_salaries)| Hard | Database | 757 | 87.06
+| 0184 |[Department Highest Salary](src/main/kotlin/g0101_0200/s0184_department_highest_salary)| Medium | Database | 637 | 76.01
+| 0183 |[Customers Who Never Order](src/main/kotlin/g0101_0200/s0183_customers_who_never_order)| Easy | Database, SQL_I_Day_1_Select | 712 | 33.67
+| 0182 |[Duplicate Emails](src/main/kotlin/g0101_0200/s0182_duplicate_emails)| Easy | Database, SQL_I_Day_10_Where | 396 | 68.40
+| 0181 |[Employees Earning More Than Their Managers](src/main/kotlin/g0101_0200/s0181_employees_earning_more_than_their_managers)| Easy | Database | 351 | 94.75
+| 0180 |[Consecutive Numbers](src/main/kotlin/g0101_0200/s0180_consecutive_numbers)| Medium | Database | 695 | 38.05
+| 0179 |[Largest Number](src/main/kotlin/g0101_0200/s0179_largest_number)| Medium | Top_Interview_Questions, String, Sorting, Greedy | 380 | 43.40
+| 0178 |[Rank Scores](src/main/kotlin/g0101_0200/s0178_rank_scores)| Medium | Database | 292 | 85.14
+| 0177 |[Nth Highest Salary](src/main/kotlin/g0101_0200/s0177_nth_highest_salary)| Medium | Database | 338 | 86.68
+| 0176 |[Second Highest Salary](src/main/kotlin/g0101_0200/s0176_second_highest_salary)| Medium | Database, SQL_I_Day_4_Union_and_Select | 219 | 92.54
+| 0175 |[Combine Two Tables](src/main/kotlin/g0101_0200/s0175_combine_two_tables)| Easy | Database, SQL_I_Day_5_Union | 473 | 54.97
+| 0174 |[Dungeon Game](src/main/kotlin/g0101_0200/s0174_dungeon_game)| Hard | Array, Dynamic_Programming, Matrix | 300 | 66.67
+| 0173 |[Binary Search Tree Iterator](src/main/kotlin/g0101_0200/s0173_binary_search_tree_iterator)| Medium | Tree, Binary_Tree, Stack, Design, Binary_Search_Tree, Iterator, Data_Structure_II_Day_17_Tree, Programming_Skills_II_Day_16, Level_2_Day_9_Binary_Search_Tree | 563 | 46.91
+| 0172 |[Factorial Trailing Zeroes](src/main/kotlin/g0101_0200/s0172_factorial_trailing_zeroes)| Medium | Top_Interview_Questions, Math, Udemy_Integers | 220 | 67.65
+| 0171 |[Excel Sheet Column Number](src/main/kotlin/g0101_0200/s0171_excel_sheet_column_number)| Easy | Top_Interview_Questions, String, Math | 310 | 30.68
 | 0169 |[Majority Element](src/main/kotlin/g0101_0200/s0169_majority_element)| Easy | Top_100_Liked_Questions, Top_Interview_Questions, Array, Hash_Table, Sorting, Counting, Divide_and_Conquer, Data_Structure_II_Day_1_Array, Udemy_Famous_Algorithm | 460 | 51.25
 | 0168 |[Excel Sheet Column Title](src/main/kotlin/g0101_0200/s0168_excel_sheet_column_title)| Easy | String, Math | 246 | 30.12
 | 0167 |[Two Sum II - Input Array Is Sorted](src/main/kotlin/g0101_0200/s0167_two_sum_ii_input_array_is_sorted)| Medium | Array, Binary_Search, Two_Pointers, Algorithm_I_Day_3_Two_Pointers, Binary_Search_I_Day_7 | 403 | 68.74

src/main/kotlin/g0101_0200/s0171_excel_sheet_column_number/readme.md

@@ -0,0 +1,51 @@
+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](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)
+
+## 171\. Excel Sheet Column Number
+
+Easy
+
+Given a string `columnTitle` that represents the column title as appears in an Excel sheet, return _its corresponding column number_.
+
+For example:
+
+A -> 1 B -> 2 C -> 3 ... Z -> 26 AA -> 27 AB -> 28 ...
+
+**Example 1:**
+
+**Input:** columnTitle = "A"
+
+**Output:** 1
+
+**Example 2:**
+
+**Input:** columnTitle = "AB"
+
+**Output:** 28
+
+**Example 3:**
+
+**Input:** columnTitle = "ZY"
+
+**Output:** 701
+
+**Constraints:**
+
+*   `1 <= columnTitle.length <= 7`
+*   `columnTitle` consists only of uppercase English letters.
+*   `columnTitle` is in the range `["A", "FXSHRXW"]`.
+
+## Solution
+
+```kotlin
+class Solution {
+    fun titleToNumber(s: String): Int {
+        var num = 0
+        var pow = 0
+        for (i in s.length - 1 downTo 0) {
+            num += Math.pow(26.0, pow++.toDouble()).toInt() * (s[i].code - 'A'.code + 1)
+        }
+        return num
+    }
+}
+```

src/main/kotlin/g0101_0200/s0172_factorial_trailing_zeroes/readme.md

@@ -0,0 +1,54 @@
+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](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)
+
+## 172\. Factorial Trailing Zeroes
+
+Medium
+
+Given an integer `n`, return _the number of trailing zeroes in_ `n!`.
+
+Note that `n! = n * (n - 1) * (n - 2) * ... * 3 * 2 * 1`.
+
+**Example 1:**
+
+**Input:** n = 3
+
+**Output:** 0
+
+**Explanation:** 3! = 6, no trailing zero.
+
+**Example 2:**
+
+**Input:** n = 5
+
+**Output:** 1
+
+**Explanation:** 5! = 120, one trailing zero.
+
+**Example 3:**
+
+**Input:** n = 0
+
+**Output:** 0
+
+**Constraints:**
+
+*   <code>0 <= n <= 10<sup>4</sup></code>
+
+**Follow up:** Could you write a solution that works in logarithmic time complexity?
+
+## Solution
+
+```kotlin
+class Solution {
+    fun trailingZeroes(n: Int): Int {
+        var base = 5
+        var count = 0
+        while (n >= base) {
+            count += n / base
+            base = base * 5
+        }
+        return count
+    }
+}
+```

src/main/kotlin/g0101_0200/s0173_binary_search_tree_iterator/readme.md

@@ -0,0 +1,92 @@
+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](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)
+
+## 173\. Binary Search Tree Iterator
+
+Medium
+
+Implement the `BSTIterator` class that represents an iterator over the **[in-order traversal](https://en.wikipedia.org/wiki/Tree_traversal#In-order_(LNR))** of a binary search tree (BST):
+
+*   `BSTIterator(TreeNode root)` Initializes an object of the `BSTIterator` class. The `root` of the BST is given as part of the constructor. The pointer should be initialized to a non-existent number smaller than any element in the BST.
+*   `boolean hasNext()` Returns `true` if there exists a number in the traversal to the right of the pointer, otherwise returns `false`.
+*   `int next()` Moves the pointer to the right, then returns the number at the pointer.
+
+Notice that by initializing the pointer to a non-existent smallest number, the first call to `next()` will return the smallest element in the BST.
+
+You may assume that `next()` calls will always be valid. That is, there will be at least a next number in the in-order traversal when `next()` is called.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2018/12/25/bst-tree.png)
+
+**Input** ["BSTIterator", "next", "next", "hasNext", "next", "hasNext", "next", "hasNext", "next", "hasNext"] [[[7, 3, 15, null, null, 9, 20]], [], [], [], [], [], [], [], [], []]
+
+**Output:** [null, 3, 7, true, 9, true, 15, true, 20, false]
+
+**Explanation:** BSTIterator bSTIterator = new BSTIterator([7, 3, 15, null, null, 9, 20]); bSTIterator.next(); // return 3 bSTIterator.next(); // return 7 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 9 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 15 bSTIterator.hasNext(); // return True bSTIterator.next(); // return 20 bSTIterator.hasNext(); // return False
+
+**Constraints:**
+
+*   The number of nodes in the tree is in the range <code>[1, 10<sup>5</sup>]</code>.
+*   <code>0 <= Node.val <= 10<sup>6</sup></code>
+*   At most <code>10<sup>5</sup></code> calls will be made to `hasNext`, and `next`.
+
+**Follow up:**
+
+*   Could you implement `next()` and `hasNext()` to run in average `O(1)` time and use `O(h)` memory, where `h` is the height of the tree?
+
+## Solution
+
+```kotlin
+import com_github_leetcode.TreeNode
+
+/*
+ * Example:
+ * var ti = TreeNode(5)
+ * var v = ti.`val`
+ * Definition for a binary tree node.
+ * class TreeNode(var `val`: Int) {
+ *     var left: TreeNode? = null
+ *     var right: TreeNode? = null
+ * }
+ */
+class BSTIterator(root: TreeNode?) {
+    private var node: TreeNode?
+
+    init {
+        node = root
+    }
+
+    operator fun next(): Int {
+        var res = -1
+        while (node != null) {
+            if (node!!.left != null) {
+                var rightMost: TreeNode? = node!!.left
+                while (rightMost!!.right != null) {
+                    rightMost = rightMost.right
+                }
+                rightMost.right = node
+                val temp: TreeNode? = node!!.left
+                node!!.left = null
+                node = temp
+            } else {
+                res = node!!.`val`
+                node = node!!.right
+                return res
+            }
+        }
+        return res
+    }
+
+    operator fun hasNext(): Boolean {
+        return node != null
+    }
+}
+
+/*
+ * Your BSTIterator object will be instantiated and called as such:
+ * var obj = BSTIterator(root)
+ * var param_1 = obj.next()
+ * var param_2 = obj.hasNext()
+ */
+```

src/main/kotlin/g0101_0200/s0174_dungeon_game/readme.md

@@ -0,0 +1,73 @@
+[![](https://img.shields.io/github/stars/javadev/LeetCode-in-Kotlin?label=Stars&style=flat-square)](https://github.com/javadev/LeetCode-in-Kotlin)
+[![](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)
+
+## 174\. Dungeon Game
+
+Hard
+
+The demons had captured the princess and imprisoned her in **the bottom-right corner** of a `dungeon`. The `dungeon` consists of `m x n` rooms laid out in a 2D grid. Our valiant knight was initially positioned in **the top-left room** and must fight his way through `dungeon` to rescue the princess.
+
+The knight has an initial health point represented by a positive integer. If at any point his health point drops to `0` or below, he dies immediately.
+
+Some of the rooms are guarded by demons (represented by negative integers), so the knight loses health upon entering these rooms; other rooms are either empty (represented as 0) or contain magic orbs that increase the knight's health (represented by positive integers).
+
+To reach the princess as quickly as possible, the knight decides to move only **rightward** or **downward** in each step.
+
+Return _the knight's minimum initial health so that he can rescue the princess_.
+
+**Note** that any room can contain threats or power-ups, even the first room the knight enters and the bottom-right room where the princess is imprisoned.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2021/03/13/dungeon-grid-1.jpg)
+
+**Input:** dungeon = \[\[-2,-3,3],[-5,-10,1],[10,30,-5]]
+
+**Output:** 7
+
+**Explanation:** The initial health of the knight must be at least 7 if he follows the optimal path: RIGHT-> RIGHT -> DOWN -> DOWN.
+
+**Example 2:**
+
+**Input:** dungeon = \[\[0]]
+
+**Output:** 1
+
+**Constraints:**
+
+*   `m == dungeon.length`
+*   `n == dungeon[i].length`
+*   `1 <= m, n <= 200`
+*   `-1000 <= dungeon[i][j] <= 1000`
+
+## Solution
+
+```kotlin
+class Solution {
+    fun calculateMinimumHP(dungeon: Array<IntArray>): Int {
+        val m = dungeon.size
+        val n = dungeon[0].size
+        val memo = Array(m) { IntArray(n) }
+        return Math.max(1, 1 - traverse(dungeon, 0, 0, memo))
+    }
+
+    private fun traverse(dungeon: Array<IntArray>, r: Int, c: Int, memo: Array<IntArray>): Int {
+        if (r == dungeon.size - 1 && c == dungeon[0].size - 1) {
+            return dungeon[r][c]
+        }
+        if (memo[r][c] != 0) {
+            return memo[r][c]
+        }
+        var res = Int.MIN_VALUE
+        if (r + 1 < dungeon.size) {
+            res = Math.max(res, traverse(dungeon, r + 1, c, memo))
+        }
+        if (c + 1 < dungeon[0].size) {
+            res = Math.max(res, traverse(dungeon, r, c + 1, memo))
+        }
+        res = Math.min(dungeon[r][c], res + dungeon[r][c])
+        memo[r][c] = res
+        return res
+    }
+}
+```