Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T. The same repeated number may be chosen from C unlimited number of times. http://www.leetcode.com/onlinejudge

leetcode_combination_sum.cpp

#include <algorithm>
using namespace std;

class Solution {
public:
    void dfs(vector<vector<int> >& ret, vector<int>& tmp, vector<int>& cands, int left, int target) {
        if (target == 0) {
            ret.push_back(tmp);
            return;
        }
        for (int i = left; i < cands.size(); ++i) {
            if (target >= cands[i]) {
                tmp.push_back(cands[i]);
                dfs(ret, tmp, cands, i, target - cands[i]);
                tmp.pop_back();
            }
        }
    }

    vector<vector<int> > combinationSum(vector<int> &candidates, int target) {
        sort(candidates.begin(), candidates.end());
        vector<vector<int> > ret;
        vector<int> tmp;
        dfs(ret, tmp, candidates, 0, target);
        return ret;
    }
};