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60 lines
1.7 KiB
60 lines
1.7 KiB
/**
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* File: subset_sum_i.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_backtracking.subset_sum_i
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import java.util.*
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/* 回溯演算法：子集和 I */
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fun backtrack(
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state: MutableList<Int>,
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target: Int,
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choices: IntArray,
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start: Int,
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res: MutableList<List<Int>?>
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) {
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// 子集和等於 target 時，記錄解
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if (target == 0) {
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res.add(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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// 剪枝二：從 start 開始走訪，避免生成重複子集
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for (i in start..<choices.size) {
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// 剪枝一：若子集和超過 target ，則直接結束迴圈
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// 這是因為陣列已排序，後邊元素更大，子集和一定超過 target
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if (target - choices[i] < 0) {
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break
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}
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// 嘗試：做出選擇，更新 target, start
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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 - choices[i], choices, i, res)
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// 回退：撤銷選擇，恢復到之前的狀態
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state.removeAt(state.size - 1)
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}
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}
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/* 求解子集和 I */
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fun subsetSumI(nums: IntArray, target: Int): List<List<Int>?> {
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val state: MutableList<Int> = ArrayList() // 狀態（子集）
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Arrays.sort(nums) // 對 nums 進行排序
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val start = 0 // 走訪起始點
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val res: MutableList<List<Int>?> = ArrayList() // 結果串列（子集串列）
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backtrack(state, target, nums, start, res)
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return res
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}
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/* Driver Code */
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fun main() {
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val nums = intArrayOf(3, 4, 5)
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val target = 9
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val res = subsetSumI(nums, target)
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println("輸入陣列 nums = ${nums.contentToString()}, target = $target")
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println("所有和等於 $target 的子集 res = $res")
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} |