【LeetCode】 39. Combination Sum 组合总和（Medium）（JAVA）
题目地址: https://leetcode.com/problems/combination-sum/
题目描述：
Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.
The same repeated number may be chosen from candidates unlimited number of times.
Note:
All numbers (including target) will be positive integers.
The solution set must not contain duplicate combinations.
Example 1:
Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
[7],
[2,2,3]
]
Example 2:
Input: candidates = [2,3,5], target = 8,
A solution set is:
[
[2,2,2,2],
[2,3,3],
[3,5]
]
题目大意
给定一个无重复元素的数组 candidates 和一个目标数 target ，找出 candidates 中所有可以使数字和为 target 的组合。
candidates 中的数字可以无限制重复被选取。
解题方法
1、对数组进行排序
2、采用递归，不断添加进 List 里面，递归结束后删除，不然 List 只增不减是有问题的
class Solution {
List<List<Integer>> res = new ArrayList<>();
List<Integer> cur = new ArrayList<>();
public List<List<Integer>> combinationSum(int[] candidates, int target) {
Arrays.sort(candidates);
cH(candidates, target, 0);
return res;
}
public void cH(int[] nums, int target, int index) {
if (target < 0) return;
if (target == 0) {
res.add(new ArrayList<>(cur));
return;
}
for (int i = index; i < nums.length; i++) {
if (target - nums[i] < 0) break;
cur.add(nums[i]);
cH(nums, target - nums[i], i);
cur.remove(cur.size() - 1);
}
}
}
执行用时 : 3 ms, 在所有 Java 提交中击败了 97.02% 的用户
内存消耗 : 40.9 MB, 在所有 Java 提交中击败了 7.65% 的用户
