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73 lines
2.3 KiB
73 lines
2.3 KiB
/**
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* File: coin_change.java
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* Created Time: 2023-07-11
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* Author: krahets (krahets@163.com)
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*/
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package chapter_dynamic_programming;
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import java.util.Arrays;
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public class coin_change {
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/* 零钱兑换：动态规划 */
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static int coinChangeDP(int[] coins, int amt) {
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int n = coins.length;
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int MAX = amt + 1;
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// 初始化 dp 表
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int[][] dp = new int[n + 1][amt + 1];
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// 状态转移：首行首列
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for (int a = 1; a <= amt; a++) {
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dp[0][a] = MAX;
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}
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// 状态转移：其余行和列
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for (int i = 1; i <= n; i++) {
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for (int a = 1; a <= amt; a++) {
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if (coins[i - 1] > a) {
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// 若超过目标金额，则不选硬币 i
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dp[i][a] = dp[i - 1][a];
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} else {
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// 不选和选硬币 i 这两种方案的较小值
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dp[i][a] = Math.min(dp[i - 1][a], dp[i][a - coins[i - 1]] + 1);
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}
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}
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}
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return dp[n][amt] != MAX ? dp[n][amt] : -1;
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}
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/* 零钱兑换：空间优化后的动态规划 */
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static int coinChangeDPComp(int[] coins, int amt) {
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int n = coins.length;
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int MAX = amt + 1;
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// 初始化 dp 表
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int[] dp = new int[amt + 1];
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Arrays.fill(dp, MAX);
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dp[0] = 0;
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// 状态转移
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for (int i = 1; i <= n; i++) {
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for (int a = 1; a <= amt; a++) {
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if (coins[i - 1] > a) {
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// 若超过目标金额，则不选硬币 i
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dp[a] = dp[a];
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} else {
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// 不选和选硬币 i 这两种方案的较小值
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dp[a] = Math.min(dp[a], dp[a - coins[i - 1]] + 1);
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}
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}
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}
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return dp[amt] != MAX ? dp[amt] : -1;
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}
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public static void main(String[] args) {
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int[] coins = { 1, 2, 5 };
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int amt = 4;
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// 动态规划
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int res = coinChangeDP(coins, amt);
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System.out.println("凑到目标金额所需的最少硬币数量为 " + res);
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// 空间优化后的动态规划
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res = coinChangeDPComp(coins, amt);
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System.out.println("凑到目标金额所需的最少硬币数量为 " + res);
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}
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}
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