leetcode--40. Combination Sum II

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

Note:

• All numbers (including target) will be positive integers.
• The solution set must not contain duplicate combinations.

For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8, 

A solution set is: 

[
  [1, 7],
  [1, 2, 5],
  [2, 6],
  [1, 1, 6]
]

class Solution {
public:
    vector> combinationSum2(vector& candidates, int target) {
        //Don't disturbing the original array
        vector can(candidates.begin(), candidates.end());
        
        //!!! Here needs to sort the array, because we need to jump the same elements
        sort(can.begin(), can.end());
        
        //Backtracing
        vector> ret;
        vector tmp;
        bt(can, tmp, target, 0, ret);
        return ret;
    }
    
private:
    void bt(vector &can, vector &tmp, int target, int start, vector> &ret){
        if(target < 0) return;
        if(target == 0) ret.push_back(tmp);
        for(int i = start; i start && can[i] == can[i-1]) continue; //To jump the same element
            tmp.push_back(can[i]);
            //Next tracing should input i+1, because reuse is illeagal
            bt(can, tmp, target-can[i], i+1, ret); 
            tmp.pop_back();
        }
    }
};