<leetcode oj> 77. Combinations

Total Accepted: 69360 Total Submissions: 206274 Difficulty: Medium

Given-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],  [up],  [1,3],  [1,4],]

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Hide TagsBacktrackingHide Similar Problems(m) combination Sum (m) permutations

Analysis:

The typical backtracking method

Class Solution {public:    void Dfs (Vector<vector<int > > &ans, vector<int> &subans, int Start, int n, int k)    {        if (subans.size () = = k)//have obtained the answer, and backtrack        {            ans.push_back (Subans);             return;//Backtracking        } for        (int i = start; I <= n; i++)        {            subans.push_back (i);            DFS (ans, subans, i + 1, n, k);            Subans.pop_back (); Backtrack minus end element        }    }    vector<vector<int> > combine (int n, int k) {        vector<vector<int > > result;        if (N < k | | k = = 0)             return result;        Vector<int> Subres;        DFS (result, subres, 1, N, k);        return result;}    ;

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<leetcode oj> 77. Combinations