LeetCode：39. Combination Sum（Medium）

1. 原题链接

https://leetcode.com/problems/combination-sum/description/

2. 题目要求

给定一个整型数组candidates[ ]和目标值target，找出数组中累加之后等于target的所有元素组合

注意：（1）数组中的每一个元素可以重复用；（2）数组中不存在重复元素；（3）数组中都是正整数

3. 解题思路

采用迭代的方法检验所有元素组合

4. 代码实现

import java.util.ArrayList;
import java.util.List;

public class CombinationSum39 {
    public static void main(String[] args) {
        CombinationSum39 cs = new CombinationSum39();
        int[] candidates = {2,3,6,7};
        for (List l1:cs.combinationSum(candidates,7)){
            System.out.println(l1.toString());
            System.out.println();
        }

    }
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        combinationSum(result,new ArrayList<Integer>(),candidates,target,0);
        return result;
    }
    public void combinationSum(List<List<Integer>> result, List<Integer> cur, int[] candidates, int target,int start) {
        if (target > 0) {
            for (int i = start;i < candidates.length;i++) { 
                cur.add(candidates[i]);
                combinationSum(result, cur, candidates, target-candidates[i],i);
                cur.remove(cur.size() - 1);
            }
        }
        if (target == 0)
            result.add(new ArrayList<Integer>(cur));
    }
}