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48 lines
1.2 KiB
48 lines
1.2 KiB
/**
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* File: fractional_knapsack.dart
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* Created Time: 2023-08-11
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* 物品 */
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class Item {
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int w; // 物品重量
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int v; // 物品價值
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Item(this.w, this.v);
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}
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/* 分數背包：貪婪 */
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double fractionalKnapsack(List<int> wgt, List<int> val, int cap) {
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// 建立物品串列，包含兩個屬性：重量、價值
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List<Item> items = List.generate(wgt.length, (i) => Item(wgt[i], val[i]));
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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.sort((a, b) => (b.v / b.w).compareTo(a.v / a.w));
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// 迴圈貪婪選擇
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double res = 0;
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for (Item 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 / 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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void main() {
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List<int> wgt = [10, 20, 30, 40, 50];
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List<int> val = [50, 120, 150, 210, 240];
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int cap = 50;
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// 貪婪演算法
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double res = fractionalKnapsack(wgt, val, cap);
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print("不超過背包容量的最大物品價值為 $res");
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}
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