mirror of
https://github.com/krahets/hello-algo.git
synced 2024-12-27 16:56:30 +08:00
a005c6ebd3
* Update avatar's link in the landing page * Bug fixes * Move assets folder from overrides to docs * Reduce figures' corner radius * Update copyright * Update header image * Krahets -> krahets * Update the landing page
55 lines
2 KiB
Java
55 lines
2 KiB
Java
/**
|
|
* File: subset_sum_i.java
|
|
* Created Time: 2023-06-21
|
|
* Author: krahets (krahets@163.com)
|
|
*/
|
|
|
|
package chapter_backtracking;
|
|
|
|
import java.util.*;
|
|
|
|
public class subset_sum_i {
|
|
/* 回溯算法:子集和 I */
|
|
static void backtrack(List<Integer> state, int target, int[] choices, int start, List<List<Integer>> res) {
|
|
// 子集和等于 target 时,记录解
|
|
if (target == 0) {
|
|
res.add(new ArrayList<>(state));
|
|
return;
|
|
}
|
|
// 遍历所有选择
|
|
// 剪枝二:从 start 开始遍历,避免生成重复子集
|
|
for (int i = start; i < choices.length; i++) {
|
|
// 剪枝一:若子集和超过 target ,则直接结束循环
|
|
// 这是因为数组已排序,后边元素更大,子集和一定超过 target
|
|
if (target - choices[i] < 0) {
|
|
break;
|
|
}
|
|
// 尝试:做出选择,更新 target, start
|
|
state.add(choices[i]);
|
|
// 进行下一轮选择
|
|
backtrack(state, target - choices[i], choices, i, res);
|
|
// 回退:撤销选择,恢复到之前的状态
|
|
state.remove(state.size() - 1);
|
|
}
|
|
}
|
|
|
|
/* 求解子集和 I */
|
|
static List<List<Integer>> subsetSumI(int[] nums, int target) {
|
|
List<Integer> state = new ArrayList<>(); // 状态(子集)
|
|
Arrays.sort(nums); // 对 nums 进行排序
|
|
int start = 0; // 遍历起始点
|
|
List<List<Integer>> res = new ArrayList<>(); // 结果列表(子集列表)
|
|
backtrack(state, target, nums, start, res);
|
|
return res;
|
|
}
|
|
|
|
public static void main(String[] args) {
|
|
int[] nums = { 3, 4, 5 };
|
|
int target = 9;
|
|
|
|
List<List<Integer>> res = subsetSumI(nums, target);
|
|
|
|
System.out.println("输入数组 nums = " + Arrays.toString(nums) + ", target = " + target);
|
|
System.out.println("所有和等于 " + target + " 的子集 res = " + res);
|
|
}
|
|
}
|