sc.next() 与 sc.nextLine() 的辨别使用：

771. 字符串中最长的连续出现的字符

import java.util.Scanner;

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

        int n = sc.nextInt();
        while(n-- > 0){
            String str = sc.next();      // sc.nextLine()  有问题的哦
            int len = str.length();
            char[] s = str.toCharArray();

            char c = '0';
            int k = 0;
            for(int i = 0; i < len; i++){
                int j = i + 1;
                while(j < len && s[j] == s[i]) j++;

                if(j - i > k){
                    k = j - i;
                    c = s[i];
                }

                i = j - 1;  //  j  位置的数也是需要计数的哦
            }

            System.out.printf("%c %d\n", c, k);
        }
    }
}

770. 单词替换

import java.util.Scanner;

public class Main{
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        String[] s = sc.nextLine().split(" ");    // sc.next() 不行的哦
        String a = sc.next();
        String b = sc.next();

        for(String c: s){
            if(c.equals(a) == true) System.out.printf("%s ", b);
            else System.out.printf("%s ", c);
        }
    }
}