Leetcode: 39. Combination Sum

Description

Given a set of candidate numbers (C) (without duplicates) 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.
• The solution set must not contain duplicate combinations.

Example

For example, given candidate set [2, 3, 6, 7] and target 7, 
A solution set is: 

[
    [7],
    [2, 2, 3]
]

思路

• dfs
• 按照下图方式剪枝，可保证没有重复
  

代码

class Solution {
public:
    vector<vector<int>> combinationSum(vector<int>& candidates, int target) {
		vector<vector<int>> res;

		sort(candidates.begin(), candidates.end());
		
		vector<int> tmp;
		dfs(candidates, target, candidates.size(), 0, res, tmp, 0);
		

		return res;
	}

	bool dfs(vector<int> &candidates, int target, int len, int t, vector<vector<int>> &res, vector<int> &tmp, int sum){
		if (sum == target){
			res.push_back(tmp);
			return true;
		}

		else if (sum < target){
			for (int i = t; i < len; ++i){
				if (sum + candidates[i] > target) return false;
				sum += candidates[i];
				tmp.push_back(candidates[i]);
				bool flag = dfs(candidates, target, len, i, res, tmp, sum);
				
				sum -= candidates[i];
				tmp.pop_back();
				
				if (flag){
					break;
				}
			}
		}

		return false;
	}
};