Leetcode#77 Combinations

原题地址

 

DFS，跟求子集合的方法类似，对于任意一个元素，要么选，要么不选。

 

代码：

vector<vector<int> > res;

void solve(vector<int> ans, int n, int curr, int left) {
  if (left == 0)
    res.push_back(ans);
  else if (n - curr + 1 >= left) {
    solve(ans, n, curr + 1, left);
    ans.push_back(curr);
    solve(ans, n, curr + 1, left - 1);
  }
}

vector<vector<int> > combine(int n, int k) {
  solve(vector<int>(), n, 1, k);
  return res;
}