被卡性能的时候要care数据类型（洛谷P5594TLE+RE的经历）

题目内容

对题目的含义理解错误

看代码~~我以为是统计一下多少人在那天，觉得这个pageNum没大用，结果是我错了……
下为代码：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int studentNum = scanner.nextInt();
        int pageNum = scanner.nextInt();
        int dayNum = scanner.nextInt();
        int[] dayArray = new int[dayNum];
        for (int i = 0; i < studentNum; i++) {
            for (int j = 0; j < pageNum; j++) {
                int temp = scanner.nextInt();
                dayArray[temp-1]++;
            }
        }
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < dayNum-1; i++) {
            result.append(dayArray[i]).append(" ");
        }
        result.append(dayArray[dayNum-1]);
        System.out.println(result);
        scanner.close();
    }
}

测试：

显然，结果是不对的……

更正后的自测

结尾一个数不对，查看代码，发现bug：

第一次提交——TLE警告

代码是这样的：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int studentNum = scanner.nextInt();
        int pageNum = scanner.nextInt();
        int dayNum = scanner.nextInt();
        int[][] dayArray = new int[dayNum][pageNum];
        for (int i = 0; i < studentNum; i++) {
            for (int j = 0; j < pageNum; j++) {
                int temp = scanner.nextInt();
                dayArray[temp-1][j]++;
            }
        }
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < dayNum-1; i++) {
            int count = 0;
            for (int j = 0; j < pageNum; j++) {
                if (dayArray[i][j] != 0) {
                    count++;
                }
            }
            result.append(count).append(" ");
        }
        int count = 0;
        for (int j = 0; j < pageNum; j++) {
            if (dayArray[dayNum-1][j] != 0) {
                count++;
            }
        }
        result.append(count);
        System.out.println(result);
        scanner.close();
    }
}

第二次提交——TLE×3暴击

本蒟蒻没想到，boolean比int还慢，醉了：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int studentNum = scanner.nextInt();
        int pageNum = scanner.nextInt();
        int dayNum = scanner.nextInt();
        boolean[][] dayArray = new boolean[dayNum][pageNum];
        for (int i = 0; i < studentNum; i++) {
            for (int j = 0; j < pageNum; j++) {
                int temp = scanner.nextInt();
                dayArray[temp-1][j]=true;
            }
        }
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < dayNum-1; i++) {
            int count = 0;
            for (int j = 0; j < pageNum; j++) {
                if (dayArray[i][j]) {
                    count++;
                }
            }
            result.append(count).append(" ");
        }
        int count = 0;
        for (int j = 0; j < pageNum; j++) {
            if (dayArray[dayNum-1][j]) {
                count++;
            }
        }
        result.append(count);
        System.out.println(result);
        scanner.close();
    }
}

第三次提交——RE，宁真狼

这次直接byte，我们既然不想优化算法，那就优化数据类型吧，哈哈：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        byte studentNum = scanner.nextByte();
        byte pageNum = scanner.nextByte();
        byte dayNum = scanner.nextByte();
        byte[][] dayArray = new byte[dayNum][pageNum];
        for (int i = 0; i < studentNum; i++) {
            for (int j = 0; j < pageNum; j++) {
                int temp = scanner.nextInt();
                dayArray[temp-1][j]++;
            }
        }
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < dayNum-1; i++) {
            byte count = 0;
            for (int j = 0; j < pageNum; j++) {
                if (dayArray[i][j] != 0) {
                    count++;
                }
            }
            result.append(count).append(" ");
        }
        byte count = 0;
        for (int j = 0; j < pageNum; j++) {
            if (dayArray[dayNum-1][j] != 0) {
                count++;
            }
        }
        result.append(count);
        System.out.println(result);
        scanner.close();
    }
}

盲测是超byte范围了，可我真的忘了byte的大小诶，测一下~~

自检：

复习一下，byte在-128~127，宁真行……

第四次提交——AC之道，在于Short

附上AC代码

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        short studentNum = scanner.nextShort();
        short pageNum = scanner.nextShort();
        short dayNum = scanner.nextShort();
        short[][] dayArray = new short[dayNum][pageNum];
        for (int i = 0; i < studentNum; i++) {
            for (int j = 0; j < pageNum; j++) {
                int temp = scanner.nextInt();
                dayArray[temp-1][j]++;
            }
        }
        StringBuilder result = new StringBuilder();
        for (int i = 0; i < dayNum-1; i++) {
            short count = 0;
            for (int j = 0; j < pageNum; j++) {
                if (dayArray[i][j] != 0) {
                    count++;
                }
            }
            result.append(count).append(" ");
        }
        short count = 0;
        for (int j = 0; j < pageNum; j++) {
            if (dayArray[dayNum-1][j] != 0) {
                count++;
            }
        }
        result.append(count);
        System.out.println(result);
        scanner.close();
    }
}