Leetcode dfs Combinations

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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],]

題意：給定兩個數字 n 和 k，給出從1...n數字中取 k個的所有可能組合
思路：dfs
遞迴的深度為 k，第 i 層的第j個節點有  n - i - j 個選擇分支
複雜度：時間 O(n^k)，空間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;}

Leetcode dfs Combinations