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;
}
};