leetcode Combination Sum解题报告

题目

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.

Note:
All numbers (including target) will be positive integers.
Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
The solution set must not contain duplicate combinations.
For example, given candidate set 2,3,6,7 and target 7,
A solution set is:
[7]
[2, 2, 3]
题目来源：https://leetcode.com/problems/combination-sum/

分析

回朔法。

代码

class Solution {
private:
    vector<vector<int>> ans;
public:
    void combinationSumHelp(vector<int>& candidates, int target, int start, vector<int>& tmpComb) {
        if(target == 0){
            ans.push_back(tmpComb);
            return;
        }
        if(target < 0)
            return;
        int len = candidates.size();
        for(int i = start; i < len; i++){
            tmpComb.push_back(candidates.at(i));
            combinationSumHelp(candidates, target - candidates.at(i), i, tmpComb);
            tmpComb.pop_back();
        }
    }
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
        sort(candidates.begin(), candidates.end());
        vector<int> tmpComb;
        combinationSumHelp(candidates, target, 0, tmpComb);
        return ans;
    }
};