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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; // 物品价值
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Item(this.w, this.v);
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}
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/* 分数背包：贪心 */
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double fractionalKnapsack(List<int> wgt, List<int> val, int cap) {
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// 创建物品列表，包含两个属性：重量、价值
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List<Item> items = List.generate(wgt.length, (i) => Item(wgt[i], val[i]));
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// 按照单位价值 item.v / item.w 从高到低进行排序
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items.sort((a, b) => (b.v / b.w).compareTo(a.v / a.w));
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// 循环贪心选择
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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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// 若剩余容量充足，则将当前物品整个装进背包
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res += item.v;
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cap -= item.w;
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} else {
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// 若剩余容量不足，则将当前物品的一部分装进背包
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res += item.v / item.w * cap;
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// 已无剩余容量，因此跳出循环
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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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// 贪心算法
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double res = fractionalKnapsack(wgt, val, cap);
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print("不超过背包容量的最大物品价值为 $res");
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}
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