1、求和

https://www.lanqiao.cn/problems/1442/learning/

解法：字符串方法的应用

import java.util.Scanner;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //在此输入您的代码...
        int sum = 0;
        for(int i = 1; i<=2019;i++) {
          String str = String.valueOf(i);
          if(str.contains("2") || str.contains("0") || str.contains("1") || str.contains("9")) {
            sum +=i;
          }
        }
        System.out.println(sum);
        scan.close();
    }
}

2、天数

https://www.lanqiao.cn/problems/542/learning/


解法：暴力

import java.util.Scanner;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //在此输入您的代码...
        int m = scan.nextInt();
        int[] day = {0,31 ,28 , 31, 30,31,30,31,31,30,31,30,31};
        System.out.println(day[m]);
        scan.close();
    }
}

3、最大缝隙

https://www.lanqiao.cn/problems/543/learning/


解法：暴力

import java.util.Scanner;
// 1:无需package
// 2: 类名必须Main, 不可修改

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //在此输入您的代码...
        int n = scan.nextInt();
        int[] num = new int[n];
        for(int i = 0; i< n ; i++) {
          num[i] = scan.nextInt();
        }
        int gap = 0;
        for(int j = 1 ; j <n;j++) {
          if(num[j] - num[j-1] > gap) {
            gap = num[j] - num[j-1];
          }
        }
        System.out.println(gap);
        scan.close();
    }
}