![](https://img2020.cnblogs.com/blog/2050289/202009/2050289-20200911200847633-329765375.png)
package com.example.lettcode.dailyexercises;
import java.util.*;
/**
* @Class CombinationSum2
* @Description 40组合总和II
* 给定一个数组 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 中的每个数字在每个组合中只能使用一次。
* <p>
* 说明:
* 所有数字(包括目标数)都是正整数。
* 解集不能包含重复的组合。
* <p>
* 示例 1:
* 输入: candidates = [10,1,2,7,6,1,5], target = 8,
* 所求解集为:
* [
* [1, 7],
* [1, 2, 5],
* [2, 6],
* [1, 1, 6]
* ]
* <p>
* 示例 2:
* 输入: candidates = [2,5,2,1,2], target = 5,
* 所求解集为:
* [
* [1,2,2],
* [5]
* ]
* @Author
* @Date 2020/9/9
**/
public class CombinationSum2 {
public static List<List<Integer>> combinationSum2(int[] candidates, int target) {
Arrays.sort(candidates);
if (candidates.length <= 0) {
return new ArrayList<>();
}
Set<List<Integer>> res = new HashSet<>();
List<Integer> integerList = new ArrayList<>();
recur(res, integerList, candidates, target, 0);
List<List<Integer>> resLists = new ArrayList<>();
for (List<Integer> integers : res) {
resLists.add(integers);
}
return resLists;
}
// 回溯
public static void recur(Set<List<Integer>> res, List<Integer> integers, int[] candidates, int target, int idx) {
// 判断找到的一组列表是否符合要求
if (target == 0) {
res.add(new ArrayList<>(integers));
return;
}
if (idx >= candidates.length) {
return;
}
// 包含当前位置的元素
if (target - candidates[idx] >= 0) {
integers.add(candidates[idx]);
recur(res, integers, candidates, target - candidates[idx], idx + 1);
integers.remove(integers.size() - 1);
}
// 跳过当前位置的元素
recur(res, integers, candidates, target, idx + 1);
}
public static void main(String[] args) {
int[] candidates = new int[]{10, 1, 2, 7, 6, 1, 5};
int target = 8;
List<List<Integer>> res = combinationSum2(candidates, target);
System.out.println("CombinationSum2 demo01 result:");
for (List<Integer> integerList : res) {
for (Integer integer : integerList) {
System.out.print("," + integer);
}
System.out.println();
}
candidates = new int[]{2, 5, 2, 1, 2};
target = 5;
res = combinationSum2(candidates, target);
System.out.println("CombinationSum2 demo02 result:");
for (List<Integer> integerList : res) {
for (Integer integer : integerList) {
System.out.print("," + integer);
}
System.out.println();
}
}
}