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Commit a9623a4

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Add Next Permutation solution with tests; mark as not recommended
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‎README.md

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- Hash Table: https://leetcode.com/problems/sequential-digits/description/
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- Hash Table: https://leetcode.com/problems/find-all-duplicates-in-an-array/
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- https://leetcode.com/problems/minimum-equal-sum-of-two-arrays-after-replacing-zeros/description/?envType=daily-question&envId=2025年05月10日
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- Bad Question : I don't recommend to solve: https://leetcode.com/problems/next-permutation/description/
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-
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### Hard Problems

‎leetcode/31.next_permutation.dart

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//! Bad Question : I don't recommend to solve
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// https://leetcode.com/problems/next-permutation/description/
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// https://www.youtube.com/watch?v=JRgIqugFhTo
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import 'package:test/test.dart';
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void main(List<String> args) {
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final stopwatch = Stopwatch()..start();
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runTests();
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Solution s = Solution();
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final nums = [2, 3, 1]; // 3,1,2
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s.nextPermutation(nums);
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stopwatch.stop();
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print('Function Execution Time : ${stopwatch.elapsedMicroseconds} micro s');
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}
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class Solution {
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void nextPermutation(List<int> nums) {
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int pivotIndex = -1;
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/// find the pivot
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for (int i = nums.length - 2; i >= 0; i--) {
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if (nums[i] < nums[i + 1]) {
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pivotIndex = i;
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break;
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}
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}
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/// find the successorIndex
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int successorIndex = -1;
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for (int i = nums.length - 1; i > pivotIndex && pivotIndex != -1; i--) {
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if (nums[i] > nums[pivotIndex]) {
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if (successorIndex == -1) {
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successorIndex = i;
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} else if (nums[i] < nums[successorIndex]) {
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successorIndex = i;
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}
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}
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}
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/// Switch Povit and successorIndex
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int temp = 0;
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if (pivotIndex != -1) {
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temp = nums[pivotIndex];
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nums[pivotIndex] = nums[successorIndex];
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nums[successorIndex] = temp;
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}
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/// Reverse The rest
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int left = pivotIndex + 1;
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int right = nums.length - 1;
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while (left < right) {
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/// Switch
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temp = nums[left];
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nums[left] = nums[right];
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nums[right] = temp;
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/// go to the next
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left++;
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right--;
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}
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print(nums);
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}
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}
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void runTests() {
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final Solution s = Solution();
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group('Next Permutation', () {
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// Basic examples from problem statement
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test('Example 1: [1,2,3] → [1,3,2]', () {
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final nums = [1, 2, 3];
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s.nextPermutation(nums);
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expect(nums, equals([1, 3, 2]));
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});
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test('Example 2: [3,2,1] → [1,2,3]', () {
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final nums = [3, 2, 1];
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s.nextPermutation(nums);
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expect(nums, equals([1, 2, 3]));
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});
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test('Example 3: [1,1,5] → [1,5,1]', () {
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final nums = [1, 1, 5];
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s.nextPermutation(nums);
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expect(nums, equals([1, 5, 1]));
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});
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// Edge cases
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test('Single element array: [5] → [5]', () {
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final nums = [5];
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s.nextPermutation(nums);
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expect(nums, equals([5]));
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});
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test('Two elements ascending: [1,2] → [2,1]', () {
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final nums = [1, 2];
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s.nextPermutation(nums);
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expect(nums, equals([2, 1]));
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});
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test('Two elements descending: [2,1] → [1,2]', () {
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final nums = [2, 1];
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s.nextPermutation(nums);
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expect(nums, equals([1, 2]));
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});
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// All same elements
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test('All same elements: [0,0,0] → [0,0,0]', () {
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final nums = [0, 0, 0];
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s.nextPermutation(nums);
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expect(nums, equals([0, 0, 0]));
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});
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// Multiple permutations
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test('Next permutation 1: [1,3,2] → [2,1,3]', () {
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final nums = [1, 3, 2];
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s.nextPermutation(nums);
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expect(nums, equals([2, 1, 3]));
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});
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test('Next permutation 2: [2,1,3] → [2,3,1]', () {
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final nums = [2, 1, 3];
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s.nextPermutation(nums);
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expect(nums, equals([2, 3, 1]));
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});
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test('Next permutation 3: [2,3,1] → [3,1,2]', () {
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final nums = [2, 3, 1];
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s.nextPermutation(nums);
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expect(nums, equals([3, 1, 2]));
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});
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// Complex cases
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test('Complex case 1: [1,5,8,4,7,6,5,3,1] → [1,5,8,5,1,3,4,6,7]', () {
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final nums = [1, 5, 8, 4, 7, 6, 5, 3, 1];
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s.nextPermutation(nums);
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expect(nums, equals([1, 5, 8, 5, 1, 3, 4, 6, 7]));
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});
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test('Complex case 2: [2,4,3,2,1] → [3,1,2,2,4]', () {
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final nums = [2, 4, 3, 2, 1];
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s.nextPermutation(nums);
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expect(nums, equals([3, 1, 2, 2, 4]));
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});
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// Maximum constraints
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test('Maximum length array: 100 elements', () {
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final nums = List.generate(100, (i) => i.isEven ? 1 : 2);
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final expected = [...nums];
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// Manually calculate expected next permutation
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expected[98] = 2;
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expected[99] = 1;
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s.nextPermutation(nums);
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expect(nums, equals(expected));
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});
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test('Maximum value elements: [100,100] → [100,100]', () {
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final nums = [100, 100];
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s.nextPermutation(nums);
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expect(nums, equals([100, 100]));
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});
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// Random cases
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test('Random case 1: [4,2,0,2,3,2,0] → [4,2,0,3,0,2,2]', () {
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final nums = [4, 2, 0, 2, 3, 2, 0];
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s.nextPermutation(nums);
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expect(nums, equals([4, 2, 0, 3, 0, 2, 2]));
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});
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test('Random case 2: [5,4,7,5,3,2] → [5,5,2,3,4,7]', () {
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final nums = [5, 4, 7, 5, 3, 2];
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s.nextPermutation(nums);
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expect(nums, equals([5, 5, 2, 3, 4, 7]));
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});
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/// From Leet Code
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test('From Leet Code 1: [2,2,7,5,4,3,2,2,1] → 2,3,1,2,2,2,4,5,7]', () {
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final nums = [2, 2, 7, 5, 4, 3, 2, 2, 1];
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s.nextPermutation(nums);
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expect(nums, equals([2, 3, 1, 2, 2, 2, 4, 5, 7]));
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});
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test('From Leet Code 1: [2,3,1,3,3] → [2,3,3,1,3]', () {
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final nums = [2, 3, 1, 3, 3];
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s.nextPermutation(nums);
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expect(nums, equals([2, 3, 3, 1, 3]));
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});
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});
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}

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