hello-algo/codes/java/chapter_greedy/coin_change_greedy.java

/**
 * File: coin_change_greedy.java
 * Created Time: 2023-07-20
 * Author: Krahets (krahets@163.com)
 */

package chapter_greedy;

import java.util.Arrays;

public class coin_change_greedy {
    /* 零钱兑换：贪心 */
    static int coinChangeGreedy(int[] coins, int amt) {
        // 假设 coins 列表有序
        int i = coins.length - 1;
        int count = 0;
        // 循环进行贪心选择，直到无剩余金额
        while (amt > 0) {
            // 找到小于且最接近剩余金额的硬币
            while (i > 0 && coins[i] > amt) {
                i--;
            }
            // 选择 coins[i]
            amt -= coins[i];
            count++;
        }
        // 若未找到可行方案，则返回 -1
        return amt == 0 ? count : -1;
    }

    public static void main(String[] args) {
        // 贪心：能够保证找到全局最优解
        int[] coins = { 1, 5, 10, 20, 50, 100 };
        int amt = 186;
        int res = coinChangeGreedy(coins, amt);
        System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
        System.out.println("凑到 " + amt + " 所需的最少硬币数量为 " + res);

        // 贪心：无法保证找到全局最优解
        coins = new int[] { 1, 20, 50 };
        amt = 60;
        res = coinChangeGreedy(coins, amt);
        System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
        System.out.println("凑到 " + amt + " 所需的最少硬币数量为 " + res);
        System.out.println("实际上需要的最少数量为 3 ，即 20 + 20 + 20");

        // 贪心：无法保证找到全局最优解
        coins = new int[] { 1, 49, 50 };
        amt = 98;
        res = coinChangeGreedy(coins, amt);
        System.out.println("\ncoins = " + Arrays.toString(coins) + ", amt = " + amt);
        System.out.println("凑到 " + amt + " 所需的最少硬币数量为 " + res);
        System.out.println("实际上需要的最少数量为 2 ，即 49 + 49");
    }
}