【Leetcode】Combinations

Given two integers n and k, return all possible combinations ofk 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],]

这个可以用深搜，在搜索过程中用vector保存中间结果，一旦满足条件就将其输出。

class Solution {public:vector<vector<int> > res;vector<int> com;void combine(int n, int k, int start){if(k==0){res.push_back(com);return;}if(start>n) return;com.push_back(start);combine(n,k-1,start+1);com.pop_back();combine(n,k,start+1);}vector<vector<int> > combine(int n, int k) {// Start typing your C/C++ solution below// DO NOT write int main() functionres.clear();com.clear();combine(n,k,1);return res;}};