algorithm-class/大厂刷题班/class35/Code03_WatchMovieMaxTime.java

package class35;

import java.util.Arrays;

// 来自小红书
// 一场电影开始和结束时间可以用一个小数组来表示["07:30","12:00"]
// 已知有2000场电影开始和结束都在同一天，这一天从00:00开始到23:59结束
// 一定要选3场完全不冲突的电影来观看，返回最大的观影时间
// 如果无法选出3场完全不冲突的电影来观看，返回-1
public class Code03_WatchMovieMaxTime {

	// 暴力方法，枚举前三场所有的可能全排列
	public static int maxEnjoy1(int[][] movies) {
		if (movies.length < 3) {
			return -1;
		}
		return process1(movies, 0);
	}

	public static int process1(int[][] movies, int index) {
		if (index == 3) {
			int start = 0;
			int watch = 0;
			for (int i = 0; i < 3; i++) {
				if (start > movies[i][0]) {
					return -1;
				}
				watch += movies[i][1] - movies[i][0];
				start = movies[i][1];
			}
			return watch;
		} else {
			int ans = -1;
			for (int i = index; i < movies.length; i++) {
				swap(movies, index, i);
				ans = Math.max(ans, process1(movies, index + 1));
				swap(movies, index, i);
			}
			return ans;
		}
	}

	public static void swap(int[][] movies, int i, int j) {
		int[] tmp = movies[i];
		movies[i] = movies[j];
		movies[j] = tmp;
	}

	// 优化后的递归解
	public static int maxEnjoy2(int[][] movies) {
		Arrays.sort(movies, (a, b) -> a[0] != b[0] ? (a[0] - b[0]) : (a[1] - b[1]));
		return process2(movies, 0, 0, 3);
	}

	public static int process2(int[][] movies, int index, int time, int rest) {
		if (index == movies.length) {
			return rest == 0 ? 0 : -1;
		}
		int p1 = process2(movies, index + 1, time, rest);
		int next = movies[index][0] >= time && rest > 0 ? process2(movies, index + 1, movies[index][1], rest - 1) : -1;
		int p2 = next != -1 ? (movies[index][1] - movies[index][0] + next) : -1;
		return Math.max(p1, p2);
	}

	// 记忆化搜索的动态规划
	public static int maxEnjoy3(int[][] movies) {
		Arrays.sort(movies, (a, b) -> a[0] != b[0] ? (a[0] - b[0]) : (a[1] - b[1]));

		int max = 0;
		for (int[] movie : movies) {
			max = Math.max(max, movie[1]);
		}

		int[][][] dp = new int[movies.length][max + 1][4];
		for (int i = 0; i < movies.length; i++) {
			for (int j = 0; j <= max; j++) {
				for (int k = 0; k <= 3; k++) {
					dp[i][j][k] = -2;// 用-2代表没算过这个过程
				}
			}
		}
		return process3(movies, 0, 0, 3, dp);
	}

	public static int process3(int[][] movies, int index, int time, int rest, int[][][] dp) {
		if (index == movies.length) {
			return rest == 0 ? 0 : -1;
		}
		if (dp[index][time][rest] != -2) {
			return dp[index][time][rest];
		}
		int p1 = process3(movies, index + 1, time, rest, dp);
		int next = movies[index][0] >= time && rest > 0 ? process3(movies, index + 1, movies[index][1], rest - 1, dp)
				: -1;
		int p2 = next != -1 ? (movies[index][1] - movies[index][0] + next) : -1;
		int ans = Math.max(p1, p2);
		dp[index][time][rest] = ans;
		return ans;
	}

	// 为了测试
	public static int[][] randomMovies(int len, int time) {
		int[][] movies = new int[len][2];
		for (int i = 0; i < len; i++) {
			int a = (int) (Math.random() * time);
			int b = (int) (Math.random() * time);
			movies[i][0] = Math.min(a, b);
			movies[i][1] = Math.max(a, b);
		}
		return movies;
	}

	public static void main(String[] args) {
		int n = 10;
		int t = 20;
		int testTime = 10000;
		System.out.println("测试开始");
		for (int i = 0; i < testTime; i++) {
			int len = (int) (Math.random() * n) + 1;
			int[][] movies = randomMovies(len, t);
			int ans1 = maxEnjoy1(movies);
			int ans2 = maxEnjoy2(movies);
			int ans3 = maxEnjoy3(movies);
			if (ans1 != ans2 || ans1 != ans3) {
				for (int[] m : movies) {
					System.out.println(m[0] + " , " + m[1]);
				}
				System.out.println(ans1);
				System.out.println(ans2);
				System.out.println("出错了");
			}
		}
		System.out.println("测试结束");
	}

}