全排列问题偷鸡做法

全排列问题偷鸡摸狗做法
用强大的（猥琐的）next_permutation

31. 下一个排列

class Solution {
public:
    void nextPermutation(vector<int>& nums) {
        next_permutation(nums.begin(),nums.end());
    }
};

46. 全排列

class Solution {
public:
    vector<vector<int>> permute(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        vector<vector<int>> res;
        do{
            res.push_back(nums);
        }while(next_permutation(nums.begin(),nums.end()));
        return res;
    }
};

47. 全排列 II

class Solution {
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        vector<vector<int>>res;
        do{
            res.push_back(nums);
        }while(next_permutation(nums.begin(),nums.end()));
        return res;
    }
};

60. 第k个排列

class Solution {
public:
    string getPermutation(int n, int k) {
        string s;
        for(int i=1;i<=n;i++) s+=to_string(i);
        
        do{
            k--;
            if(!k)break;
        }while(next_permutation(s.begin(),s.end()));
        
        return s;
    }
};