[Leetcode] combinations [38]

Title

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],]

Link to original topic (point me)

Thinking of solving problems

Combinatorial problem, the old idea---recursive plus cycle, this is the combination of simple.

Code implementation

Class Solution {public:    vector<vector<int> > Combine (int n, int k) {        vector<vector<int> > ret;        Helper (k, 1, N, vector<int> (), ret);        return ret;    }    void Helper (int k, int start, int n, vector<int> part, vector<vector<int> > &ret) {        if (k==part.s Ize ()) {            ret.push_back (part);            return;        }        for (int i=start; i<=n; ++i) {            part.push_back (i);            Helper (k, i+1, N, part, ret);            Part.pop_back ();}}    ;

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[Leetcode] combinations [38]