每日一题ing，今天是个medium题322. Coin Change

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        int len=nums.size();
        vector<vector<int>> ret;
        dfs(nums,ret,0,len);
        return ret;
    }

    void dfs(vector<int>& nums,vector<vector<int>>& ret,int first,int len){
        if(first==len){
            ret.push_back(nums);
            return;
        }
        for(int i=first;i<len;i++){
            swap(nums[i],nums[first]);
            dfs(nums,ret,first+1,len);
            swap(nums[i],nums[first]);
        }
    }
};