leetcode31. 下一个排列

public void nextPermutation(int[] nums) {
        if(nums.length == 1) return;
		if(nums.length == 2) {swap(nums, 0, 1); return;}
		int len = nums.length;
		int index = len-2;
        for(; index >= 0; index --) {
        	if(nums[index] < nums[index+1])
        		break;
        }
        if(index < 0) {
        	reserve(nums, 0, len-1);
        	return;
        }
        for(int i = len-1; i > index; i --) {
        	if(nums[i] > nums[index]) {
        		swap(nums, i, index);
        		reserve(nums, index+1, len-1);
                return;
        	}
        }
    }
    public void swap(int[] nums, int n, int m) {
		int tmp = nums[n];
		nums[n] = nums[m];
		nums[m] = tmp;
	}
    public void reserve(int[] nums, int n, int m) {
		while(n < m) swap(nums,n++,m--);
	}