LeetCode-77. 组合

给定两个整数 n 和 k，返回 1 ... n 中所有可能的 k 个数的组合。

示例:

输入: n = 4, k = 2
输出:
[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

回溯算法：

#include <iostream>
#include <vector>
using namespace std;

class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>>res;
        vector<int> tar;
        backTrace(0,n,tar,k,res);
        return res;
    }

    void backTrace(int first,int n,vector<int>&dest, int k, vector<vector<int>>& res){
        if(dest.size()==k){
            res.push_back(dest);
            return;
        }
        for(int i=first+1;i<=n;i++){
            vector<int>tmp (dest);
            dest.push_back(i);
            backTrace(i,n,dest,k,res);
            dest = tmp;
        }
    }
};

int main(){
    Solution *ps = new Solution();
    vector<vector<int>>res = ps->combine(4,3);
    for(int i=0;i<res.size();i++){
        vector<int> it = res[i];
        for(int j=0;j<it.size();j++){
            cout<<it[j];
        }
        cout<<endl;
    }
    return 0;
}