题解 | #统计字符串中字母出现次数#

方法一：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        StringBuilder sb = new StringBuilder();
        int count=0;
        for(int i = str.length()-1; i>=0; i--){
            sb.append(str.charAt(i));
            count++;
            if(count % 3 == 0 && i != 0) sb.append(',');
        }
        System.out.println(sb.reverse().toString());

    }
}

方法二,击败双百：

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.next();

        StringBuilder sb = new StringBuilder(str);
        for(int i = str.length()-3; i>=0; i-=3){
            sb.insert(i,',');
        }
        System.out.println(sb.toString());

    }
}