Next Permutation

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.

1,2,3 → 1,3,2
3,2,1 → 1,2,3
1,1,5 → 1,5,1

Java

public class Solution {
    public void nextPermutation(int[] nums) {
        //Find the longest non-increasing suffix
        int i = nums.length - 1;
        while(i > 0 && nums[i - 1] >= nums[i]) {
            i--;
        }

        if(i == 0) {
            reverseArray(nums, 0, nums.length - 1);
            return;
        }

        // Find rightmost element that exceeds the pivot
        int pivot = nums[i - 1];
        int j = nums.length - 1;

        while(nums[j] <= pivot) {
            j--;
        }

        // Swap the pivot with nums[j]
        int temp = nums[j];
        nums[j] = nums[i - 1];
        nums[i - 1] = temp;

        // Reverse the suffix
        reverseArray(nums, i, nums.length - 1);
    }
    public void reverseArray(int[] nums, int start, int end) {
        while(start < end) {
            int temp = nums[start];
            nums[start++] = nums[end];
            nums[end--] = temp;
        }
    }
}