챕터 11-6 연습문제

[pej4303]

• [11-6] 다음의 코드는 성적평균의 범위별로 학생 수를 세기 위한 것이다. TreeSet이 학생들의 평균을 기준으로 정렬하도록 compare(Object o1, Object o2)와 평균점수의 범위를 주면 해당 범위에 속한 학생의 수를 반환하는 getGroupCount()를 완성하라.
• [Hint] TreeSet의 subSet(Object from, Object to) 를 사용하라.

import java.util.*;
class Student implements Comparable {
    String name;
    int ban;
    int no;
    int kor;
    int eng;
    int math;
    Student(String name, int ban, int no, int kor, int eng, int math) {
        this.name = name;
        this.ban = ban;
        this.no = no;
        this.kor = kor;
        this.eng = eng;
        this.math = math;
    }
    int getTotal() {
        return kor+eng+math;
    }
    float getAverage() {
        return (int)((getTotal()/ 3f)*10+0.5)/10f;
    }
    public String toString() {
        return name
        +","+ban
        +","+no
        +","+kor
        +","+eng
        +","+math
        +","+getTotal()
        +","+getAverage()
        ;
    }
    public int compareTo(Object o) {
        if(o instanceof Student) {
            Student tmp = (Student)o;
            
            return name.compareTo(tmp.name);
        } else {
            return -1;
        }
    }
} // class Student
class Exercise11_6 {
    static int getGroupCount(TreeSet tset, int from, int to) {
        /*
        (1) 알맞은 코드를 넣어 완성하시오.
        */
    }
    public static void main(String[] args) {
        TreeSet set = new TreeSet(new Comparator() {
        public int compare(Object o1, Object o2) {
            /*
            (2) 알맞은 코드를 넣어 완성하시오.
            */
        }
    });
    
   set.add(new Student("홍길동",1,1,100,100,100)); 
   set.add(new Student("남궁성",1,2,90,70,80)); 
   set.add(new Student("김자바",1,3,80,80,90)); 
   set.add(new Student("이자바",1,4,70,90,70)); 
   set.add(new Student("안자바",1,5,60,100,80)); 
    
    Iterator it = set.iterator();
    
    while(it.hasNext())
        System.out.println(it.next());

    System.out.println("[60~69] :"+getGroupCount(set,60,70));
    System.out.println("[70~79] :"+getGroupCount(set,70,80));
    System.out.println("[80~89] :"+getGroupCount(set,80,90));
    System.out.println("[90~100] :"+getGroupCount(set,90,101));
    }
}

[실행결과]
이자바,1,4,70,90,70,230,76.7
남궁성,1,2,90,70,80,240,80.0
김자바,1,3,80,80,90,250,83.3
홍길동,1,1,100,100,100,300,100.0
[60~69] :0
[70~79] :1
[80~89] :2
[90~100] :1

출처

• Java의 정석

[kha212]

작성중.. (5번째 요소 추가 도중 에러 발생)

    static int getGroupCount(TreeSet tset, int from, int to) {
		//System.out.println(tset);
		TreeSet ts = (TreeSet) tset.subSet(from, to);
        return ts.size();
    }
	
    public static void main(String[] args) {
		TreeSet set = new TreeSet(new Comparator() {
	        public int compare(Object o1, Object o2) {
	            Student2 s1 = (Student2) o1;
	            Student2 s2 = (Student2) o2;
	            return (Float.compare(s1.getAverage(), s2.getAverage()));
		    }
	    });
	    
	   set.add(new Student2("홍길동",1,1,100,100,100)); 
	   set.add(new Student2("남궁성",1,2,90,70,80)); 
	   set.add(new Student2("김자바",1,3,80,80,90)); 
	   set.add(new Student2("이자바",1,4,70,90,70)); 
	   set.add(new Student2("안자바",1,5,60,100,80)); 
	    
	    Iterator it = set.iterator();
	    
	    while(it.hasNext())
	        System.out.println(it.next());
	
	    System.out.println("[60~69] :"+getGroupCount(set,60,70));
	    System.out.println("[70~79] :"+getGroupCount(set,70,80));
	    System.out.println("[80~89] :"+getGroupCount(set,80,90));
	    System.out.println("[90~100] :"+getGroupCount(set,90,101));
    }

[pej4303]

static int getGroupCount(TreeSet<Student> tset, int from, int to) {
    // 참조형(Student) TreeSet이기때문에 Student 인스턴스를 만들어서 넣어줘야함
    return tset.subSet(new Student("",0,0,from,from,from), new Student("",0,0,to,to,to)).size();
}

public static void exam06() {
   // TreeSet
   TreeSet<Student> set = new TreeSet<>(new Comparator<Student>() {
       public int compare(Student s1, Student s2) {
           return (int) (s1.getAverage() - s2.getAverage());
       }
   });
    
   set.add(new Student("홍길동",1,1,100,100,100)); 
   set.add(new Student("남궁성",1,2,90,70,80)); 
   set.add(new Student("김자바",1,3,80,80,90)); 
   set.add(new Student("이자바",1,4,70,90,70)); 
   set.add(new Student("안자바",1,5,60,100,80));
   
   Iterator<Student> it = set.iterator();
   
   // 안자바 평균점수가 남궁성과 80점으로 동일하여 compare 결과 중복으로 판정되어 4개만 출력됨
   while (it.hasNext()) {
       System.out.println(it.next());
   }

   System.out.println("[60~69] : " + getGroupCount(set,60,70));
   System.out.println("[70~79] : " + getGroupCount(set,70,80));
   System.out.println("[80~89] : " + getGroupCount(set,80,90)); 
   System.out.println("[90~100] : " + getGroupCount(set,90,101));
}

[실행결과]
이자바,1,4,70,90,70,230,76.7
남궁성,1,2,90,70,80,240,80.0
김자바,1,3,80,80,90,250,83.3
홍길동,1,1,100,100,100,300,100.0
[60~69] : 0
[70~79] : 1
[80~89] : 2
[90~100] : 1