permutation sequence

Author: chen0040

.idea/workspace.xml

@@ -427,3 +427,4 @@ codes may not be optimized
 
 1. [Largest Divisible Subset](https://leetcode.com/problems/largest-divisible-subset/description/)
 1. [Partition Equal Subset Sum](https://leetcode.com/problems/partition-equal-subset-sum/description/)
+1. [Permutation Sequence](https://leetcode.com/problems/permutation-sequence/description/)

README.md

@@ -0,0 +1,44 @@
+package com.github.chen0040.leetcode.day21.medium;
+
+
+import java.util.ArrayList;
+import java.util.List;
+
+
+/**
+ * Created by xschen on 16/8/2017.
+ *
+ * link: https://leetcode.com/problems/permutation-sequence/description/
+ */
+public class PermutationSequence {
+   public class Solution {
+      String target;
+      int count;
+      public String getPermutation(int n, int k) {
+         int[] factorial = new int[n];
+         factorial[0] = 1;
+         for(int i = 1; i < n; ++i) {
+            factorial[i] = factorial[i-1] * i;
+         }
+
+         k--;
+
+         List<Integer> nums = new ArrayList<Integer>();
+         for(int i=0; i < n; ++i) {
+            nums.add(i+1);
+         }
+         StringBuilder sb = new StringBuilder();
+         for(int i=1; i <= n; ++i) {
+            int index = k / factorial[n-i];
+            sb.append(nums.get(index));
+            nums.remove(nums.get(index));
+            k -= index * factorial[n-i];
+         }
+
+         return sb.toString();
+      }
+
+
+
+   }
+}