Combination Sum II [LeetCode]

Problem description: http://oj.leetcode.com/problems/combination-sum-ii/

Basic idea: use recursive approach, remember to avoid duplicate item.

class Solution {
public:
    bool isExist(vector<vector<int> > &combinations, vector<int> &item) {
        for(auto com: combinations){
            if(com.size() == item.size()){
                int k;
                for(k = 0; k < com.size(); k++){
                    if(com[k] != item[k])
                        break;
                }
                if(k == com.size())
                    return true;
            }
        }  
        return false;
    }
    vector<vector<int> > combinationSum2(vector<int> &num, int target) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        vector<vector<int> >  combinations;
        std::sort(num.begin(), num.end());
        int is_target_equal_to_num = 0;
        for(int i = 0; i < num.size(); i ++){
            if(num[i] == target && !is_target_equal_to_num){
                is_target_equal_to_num = 1;
                vector<int> combination(1, target);
                combinations.push_back(combination);
            }else if(num[i] > target) {
                break;
            }else {
                vector<int> sub_num(num.begin() + i + 1, num.end());
                vector<vector<int> > sub_combinations = combinationSum2(sub_num, target - num[i]);
                for (auto item : sub_combinations) {
                    item.insert(item.begin(), num[i]);
                    if(!isExist(combinations, item))
                        combinations.push_back(item);
                }
            }
        }
        
        return combinations;
    }
};