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51 lines
1.4 KiB
51 lines
1.4 KiB
/**
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* File: fractional_knapsack.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_greedy
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/* 物品 */
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class Item(
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val w: Int, // 物品
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val v: Int // 物品價值
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)
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/* 分數背包：貪婪 */
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fun fractionalKnapsack(wgt: IntArray, _val: IntArray, c: Int): Double {
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// 建立物品串列，包含兩個屬性：重量、價值
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var cap = c
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val items = arrayOfNulls<Item>(wgt.size)
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for (i in wgt.indices) {
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items[i] = Item(wgt[i], _val[i])
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}
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// 按照單位價值 item.v / item.w 從高到低進行排序
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items.sortBy { item: Item? -> -(item!!.v.toDouble() / item.w) }
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// 迴圈貪婪選擇
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var res = 0.0
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for (item in items) {
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if (item!!.w <= cap) {
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// 若剩餘容量充足，則將當前物品整個裝進背包
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res += item.v
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cap -= item.w
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} else {
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// 若剩餘容量不足，則將當前物品的一部分裝進背包
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res += item.v.toDouble() / item.w * cap
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// 已無剩餘容量，因此跳出迴圈
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break
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}
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}
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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 wgt = intArrayOf(10, 20, 30, 40, 50)
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val _val = intArrayOf(50, 120, 150, 210, 240)
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val cap = 50
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// 貪婪演算法
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val res = fractionalKnapsack(wgt, _val, cap)
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println("不超過背包容量的最大物品價值為 $res")
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} |