practice leetcode 31

README.md

@@ -15,6 +15,7 @@ This is the repository records my Algorithms & Data structures learning with
 | 25  | [Reverse Nodes in k-Group](https://leetcode.com/problems/reverse-nodes-in-k-group/)                                     | [Js](./sourceFile/Js/25_ReverseNodesInKGroup.js)                                                                                | hard       | LinkedList      |
 | 26  | [Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/)               | [Js](./sourceFile/Js/26_RemoveDuplicatesFromSortedArray.js) [Ts](./sourceFile/typescript/26_RemoveDuplicatesFromSortedArray.ts) | easy       | Array           |
 | 27  | [Remove Element](https://leetcode.com/problems/remove-element/)                                                         | [Js](./sourceFile/Js/27_RemoveElements.js) [Ts](./sourceFile/typescript/27_RemoveElement.ts)                                    | easy       | Double Pointers |
+| 31  | [Next Permutation](https://leetcode.com/problems/next-permutation/)                                                     | [Ts](./sourceFile/typescript/31_NextPermutation.ts)                                                                             | medium     | Array           |
 | 35  | [Search Insert Position](https://leetcode.com/problems/search-insert-position/)                                         | [Js](./sourceFile/Js/35_SearchInsertPosition.js)                                                                                | easy       | Binary Search   |
 | 46  | [Permutations](https://leetcode.com/problems/permutations/)                                                             | [Ts](./sourceFile/typescript/46_Permutations.ts)                                                                                | medium     | Backtracking    |
 | 77  | [Combinations](https://leetcode.com/problems/combinations/)                                                             | [Ts](./sourceFile/typescript/77_Combinations.ts)                                                                                | medium     | Backtracking    |

sourceFile/typescript/31_NextPermutation.ts

@@ -0,0 +1,45 @@
+// @algorithm @lc id=31 lang=typescript
+// @title next-permutation
+// @test([1,2,3])=[1,3,2]
+// @test([3,2,1])=[1,2,3]
+// @test([1,1,5])=[1,5,1]
+/**
+ Do not return anything, modify nums in-place instead.
+ */
+function nextPermutation(nums: number[]): void {
+  if (nums.length === 1) return;
+  if (nums.length === 2) {
+    nums.reverse();
+    return;
+  }
+
+  let i = nums.length - 2;
+  while (i >= 0 && nums[i] >= nums[i + 1]) {
+    i--;
+  }
+
+  if (i >= 0) {
+    let j = nums.length - 1;
+    while (j >= 0 && nums[j] <= nums[i]) {
+      j--;
+    }
+
+    let temp = nums[i];
+    nums[i] = nums[j];
+    nums[j] = temp;
+  }
+
+  for (
+    let left = i + 1, right = nums.length - 1;
+    left < right;
+    left++, right--
+  ) {
+    let temp = nums[left];
+    nums[left] = nums[right];
+    nums[right] = temp;
+  }
+}
+
+const nums = [1, 5, 1];
+nextPermutation(nums);
+console.log(nums);