31. 下一个排列.java

class Solution {
    public void nextPermutation(int[] nums) {
        int n = nums.length;
        int i = n - 2;
        for (; i >= 0; i--) {
            if (nums[i] < nums[i + 1]) {
                break;
            }
        }
        if (i >= 0) {
            int j = nums.length - 1;
            for (; j > i; j--) {
                if (nums[j] > nums[i]) {
                    break;
                }
            }
            swap(nums, i, j);
        }
        reverse(nums, i + 1);
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }

    private void reverse(int[] nums, int start) {
        int i = start, j = nums.length - 1;
        while (i < j) {
            swap(nums, i, j);
            i++;
            j--;
        }
    }
}