algorithm-class/MCA算法突击课/第01期/mca_test/Code02_CoinsWayEveryPaperDifferent.java

package 第01期.mca_test;

public class Code02_CoinsWayEveryPaperDifferent {

	public static int coinWays(int[] arr, int aim) {
		return process(arr, 0, aim);
	}

	// arr[index....] 组成正好rest这么多的钱，有几种方法
	public static int process(int[] arr, int index, int rest) {
		if (rest < 0) {
			return 0;
		}
		if (index == arr.length) { // 没钱了！
			return rest == 0 ? 1 : 0;
		} else {
			return process(arr, index + 1, rest) + process(arr, index + 1, rest - arr[index]);
		}
	}

	public static int dp(int[] arr, int aim) {
		if (aim == 0) {
			return 1;
		}
		int N = arr.length;
		int[][] dp = new int[N + 1][aim + 1];
		dp[N][0] = 1;
		for (int index = N - 1; index >= 0; index--) {
			for (int rest = 0; rest <= aim; rest++) {
				dp[index][rest] = dp[index + 1][rest] + (rest - arr[index] >= 0 ? dp[index + 1][rest - arr[index]] : 0);
			}
		}
		return dp[0][aim];
	}

	// 为了测试
	public static int[] randomArray(int maxLen, int maxValue) {
		int N = (int) (Math.random() * maxLen);
		int[] arr = new int[N];
		for (int i = 0; i < N; i++) {
			arr[i] = (int) (Math.random() * maxValue) + 1;
		}
		return arr;
	}

	// 为了测试
	public static void printArray(int[] arr) {
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i] + " ");
		}
		System.out.println();
	}

	// 为了测试
	public static void main(String[] args) {
		int maxLen = 20;
		int maxValue = 30;
		int testTime = 1000000;
		System.out.println("测试开始");
		for (int i = 0; i < testTime; i++) {
			int[] arr = randomArray(maxLen, maxValue);
			int aim = (int) (Math.random() * maxValue);
			int ans1 = coinWays(arr, aim);
			int ans2 = dp(arr, aim);
			if (ans1 != ans2) {
				System.out.println("Oops!");
				printArray(arr);
				System.out.println(aim);
				System.out.println(ans1);
				System.out.println(ans2);
				break;
			}
		}
		System.out.println("测试结束");
	}

}