Leetcode dfs Combinations, leetcode

Leetcode dfs Combinations, leetcode

Combinations Total Accepted: 18327 Total Submissions: 60479My Submissions

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],]

Given two numbers n and k, all possible combinations of k numbers are given from 1... n.
Train of Thought: dfs
The recursive depth is k, and the j-th node of the I-layer has n-I-j selected branches.
Complexity: time O (n ^ k), Space O (k)

vector<vector<int> > res;int nn, kk;void dfs(int cur, int start, vector<int> &path){if(cur == kk ){res.push_back(path);}for(int i = start; i <= nn; i++){path.push_back(i);dfs(cur + 1, i + 1, path);path.pop_back();}}vector<vector<int> > combine(int n, int k){nn = n, kk = k;vector<int> path;dfs(0, 1, path);return res;}