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/**
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* File: subset_sum_i_naive.java
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* Created Time: 2023-06-21
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* Author: krahets (krahets@163.com)
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*/
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package chapter_backtracking;
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import java.util.*;
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public class subset_sum_i_naive {
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/* 回溯演算法：子集和 I */
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static void backtrack(List<Integer> state, int target, int total, int[] choices, List<List<Integer>> res) {
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// 子集和等於 target 時，記錄解
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if (total == target) {
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res.add(new ArrayList<>(state));
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return;
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}
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// 走訪所有選擇
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for (int i = 0; i < choices.length; i++) {
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// 剪枝：若子集和超過 target ，則跳過該選擇
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if (total + choices[i] > target) {
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continue;
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}
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// 嘗試：做出選擇，更新元素和 total
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state.add(choices[i]);
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// 進行下一輪選擇
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backtrack(state, target, total + choices[i], choices, res);
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// 回退：撤銷選擇，恢復到之前的狀態
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state.remove(state.size() - 1);
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}
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}
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/* 求解子集和 I（包含重複子集） */
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static List<List<Integer>> subsetSumINaive(int[] nums, int target) {
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List<Integer> state = new ArrayList<>(); // 狀態（子集）
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int total = 0; // 子集和
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List<List<Integer>> res = new ArrayList<>(); // 結果串列（子集串列）
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backtrack(state, target, total, nums, res);
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return res;
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}
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public static void main(String[] args) {
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int[] nums = { 3, 4, 5 };
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int target = 9;
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List<List<Integer>> res = subsetSumINaive(nums, target);
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System.out.println("輸入陣列 nums = " + Arrays.toString(nums) + ", target = " + target);
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System.out.println("所有和等於 " + target + " 的子集 res = " + res);
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System.out.println("請注意，該方法輸出的結果包含重複集合");
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}
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}
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