[LeetCode] Combinations (bfs)

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],
]
方法：把用queue实现bfs，改为用vector自己实现bfs，没有用额外的内存来存储中间值：

class Solution {
public:
    vector<vector<int> > combine(int n, int k) {
        vector<vector<int> > res;
        if(n<1 || k<1)
          return res;

        vector<int> v,v0;
        for(int i=1;i<=n;i++){
            v.push_back(i);
            res.push_back(v);
            v.clear();
        }//end for

        while(!res.empty()){
            v = res[0];
            res.erase(res.begin());
            if(v.size() == k){
                res.push_back(v);
                break;
            }else{
                v0 = v;
                for(int i=1;i<=n;i++){
                    if(find(v.begin(),v.end(),i)==v.end()){
                        v.push_back(i);
                        sort(v.begin(),v.end());
                        if(find(res.begin(),res.end(),v)==res.end())
                           res.push_back(v);
                        v = v0;
                    }
                }//end for
            }

        }//end while
        return res;
    }//end func
};

[LeetCode] Combinations (bfs)