leetcode--

1.题目描述

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

2.解法分析

一种类似于深度搜索的概念，一旦找到满足的解，立马加入到结果中，用一个数组保存中间结果

class Solution {
public:
    vector<vector<int> > combine(int n, int k) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int>> result;
        if(n<k||n<=0||k<0)return result;
        vector<int> cur;
        myCombine(result,cur,1,n,k);
        return result;
    }
    void myCombine(vector<vector<int> > &result,vector<int> &cur,int start,int n,int k)
    {

        if(k==0){result.push_back(cur);return;}
        if(start>n)return;

        cur.push_back(start);
        myCombine(result,cur,start+1,n,k-1);
        cur.pop_back();
        myCombine(result,cur,start+1,n,k);
    }

};