已知字符串String s=解梓n + 闫励鑫n + 王炳权n + 狄泉宇n + 杨士豪n + 王帅雨n + 刘亚隆n + 高蒙蒙n + 王鑫n + 闫一帆n + 郭江炜n + 靳炎睿n + 成宗汶n + 王志豪n +

1. 找出班级所有姓氏

String[] names = s.split("\n");
List<String> lastNames = new ArrayList<>();
for(String name : names){
    String lastName = name.substring(0,1);
    lastNames.add(lastName);
}

2. 将每个姓氏的学生找出，各自放入List集合；组合成一个List<List>集合

List<List<String>> studentsByLastName = new ArrayList<>();
for(String lastName : lastNames){
    List<String> students = new ArrayList<>();
    for(String name : names){
        if(name.startsWith(lastName)){
            students.add(name);
        }
    }
    studentsByLastName.add(students);
}

3. 找出学生最多的姓氏是什么，有多少人

int maxCount = 0;
String maxLastName = "";
for(List<String> students : studentsByLastName){
    int count = students.size();
    if(count > maxCount){
        maxCount = count;
        maxLastName = students.get(0).substring(0,1);
    }
}
System.out.println("姓氏为" + maxLastName + "的学生最多，共" + maxCount + "人");

4）有哪些姓氏，只有一名同学

List<String> lonelyLastNames = new ArrayList<>();
for(List<String> students : studentsByLastName){
    if(students.size() == 1){
        lonelyLastNames.add(students.get(0).substring(0,1));
    }
}
System.out.println("只有一名同学的姓氏有：" + lonelyLastNames);
``