31. Next Permutation（js）

31. 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 and use only constant 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

题意：找到下一组全排列

代码如下：

/**
 * @param {number[]} nums
 * @return {void} Do not return anything, modify nums in-place instead.
 */
var nextPermutation = function(nums) {
        let n=nums.length;
        let i,j;
        for(  i=n-2;i>=0;i--){
//             从后往前遍历，若后一项大于前一项时
            if(nums[i+1]>nums[i]){
                for(  j=n-1;j>i;j--){
                    if(nums[j]>nums[i]) break;
                }
                swap(nums,i,j);
                reverse(nums,i+1);
                return;
            }
        }
        nums.reverse();
};
// 交换
var swap=function(nums,i,j){
    let tmp=nums[i];
    nums[i]=nums[j];
    nums[j]=tmp;
};
// 翻转
var reverse=function(nums,i){
    let n=nums.length-1;
    while(i<n){
        swap(nums,i,n);
        i++;
        n--;
    }
    
}