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56 lines
2.0 KiB
56 lines
2.0 KiB
/**
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* File: coin_change_greedy.java
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* Created Time: 2023-07-20
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* Author: krahets (krahets@163.com)
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*/
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package chapter_greedy;
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import java.util.Arrays;
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public class coin_change_greedy {
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/* 零錢兌換：貪婪 */
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static int coinChangeGreedy(int[] coins, int amt) {
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// 假設 coins 串列有序
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int i = coins.length - 1;
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int count = 0;
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// 迴圈進行貪婪選擇，直到無剩餘金額
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while (amt > 0) {
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// 找到小於且最接近剩餘金額的硬幣
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while (i > 0 && coins[i] > amt) {
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i--;
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}
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// 選擇 coins[i]
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amt -= coins[i];
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count++;
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}
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// 若未找到可行方案，則返回 -1
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return amt == 0 ? count : -1;
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}
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public static void main(String[] args) {
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// 貪婪：能夠保證找到全域性最優解
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int[] coins = { 1, 5, 10, 20, 50, 100 };
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int amt = 186;
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int res = coinChangeGreedy(coins, amt);
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System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
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System.out.println("湊到 " + amt + " 所需的最少硬幣數量為 " + res);
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// 貪婪：無法保證找到全域性最優解
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coins = new int[] { 1, 20, 50 };
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amt = 60;
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res = coinChangeGreedy(coins, amt);
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System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
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System.out.println("湊到 " + amt + " 所需的最少硬幣數量為 " + res);
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System.out.println("實際上需要的最少數量為 3 ，即 20 + 20 + 20");
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// 貪婪：無法保證找到全域性最優解
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coins = new int[] { 1, 49, 50 };
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amt = 98;
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res = coinChangeGreedy(coins, amt);
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System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
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System.out.println("湊到 " + amt + " 所需的最少硬幣數量為 " + res);
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System.out.println("實際上需要的最少數量為 2 ，即 49 + 49");
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}
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}
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