技術標籤：javajava演算法

3.1 比較器

• 返回負數的時候，第一個引數排在前面
• 返回正數的時候，第二個引數排在前面
• 返回0的時候，誰在前面無所謂（預設排序）

定義 Student 類，以年齡 age 逆序輸出。寫了兩種不同的比較器格式，習慣用第一種。

import java.util.*;

public class comparatorDemo {
	
	public static class Student {
		public String name;
		public int id;
		public int age;
		
		public Student (String name, int id, int age) {
			this.name = name;
			this.id = id;
			this.age = age;
		}
	}
	
	public static void main (String[] args) {
		Student std1 = new Student("摸魚人生", 1, 16);
		Student std2 = new Student("多快樂", 2, 22);
		Student std3 = new Student("大海的對面", 3, 18);
		Student std4 = new Student("沒有自由", 4, 25);
		
		Student[] stdArr = new Student[] {std1, std2, std3, std4};
		
		for (int i = 0; i < stdArr.length; i++) {
			System.out.println(stdArr[i].name + " " + stdArr[i].id + " " + stdArr[i].age);
		}
		System.out.println("============");
		
		Arrays.sort(stdArr, new Comparator<Student>() {			// 返回負數的時候，第一個引數排在前面
			public int compare (Student std1, Student std2) {	// 返回正數的時候，第二個引數排在前面
				return std2.age - std1.age;						// 返回0的時候，誰在前面無所謂（預設排序）
			}			
		});
	
		for (int i = 0; i < stdArr.length; i++) {
			System.out.println(stdArr[i].name + " " + stdArr[i].id + " " + stdArr[i].age);
		}
	}	
}
 

import java.util.*;

public class comparatorDemo {
	
	public static class Student {
		public String name;
		public int id;
		public int age;
		
		public Student (String name, int id, int age) {
			this.name = name;
			this.id = id;
			this.age = age;
		}
	}
	
	public static void main (String[] args) {
		Student std1 = new Student("摸魚人生", 1, 16);
		Student std2 = new Student("多快樂", 2, 22);
		Student std3 = new Student("大海的對面", 3, 18);
		Student std4 = new Student("沒有自由", 4, 25);
		
		Student[] stdArr = new Student[] {std1, std2, std3, std4};
		
		for (int i = 0; i < stdArr.length; i++) {
			System.out.println(stdArr[i].name + " " + stdArr[i].id + " " + stdArr[i].age);
		}
		System.out.println("============");
		
		Arrays.sort(stdArr, new studentComp());
	
		for (int i = 0; i < stdArr.length; i++) {
			System.out.println(stdArr[i].name + " " + stdArr[i].id + " " + stdArr[i].age);
		}
	}
	
	public static class studentComp implements Comparator<Student> {
		public int compare (Student std1, Student std2) {
			return std1.age - std2.age;
		}
	}	
}
 

第三種方式是以大根堆的結構彈出。

import java.util.*;

public class comparatorDemo {
	
	public static class Student {
		public String name;
		public int id;
		public int age;
		
		public Student (String name, int id, int age) {
			this.name = name;
			this.id = id;
			this.age = age;
		}
	}
	
	public static void main (String[] args) {
		Student std1 = new Student("摸魚人生", 1, 16);
		Student std2 = new Student("多快樂", 2, 22);
		Student std3 = new Student("大海的對面", 3, 18);
		Student std4 = new Student("沒有自由", 4, 25);
		
		Student[] stdArr = new Student[] {std1, std2, std3, std4};
		
		for (int i = 0; i < stdArr.length; i++) {
			System.out.println(stdArr[i].name + " " + stdArr[i].id + " " + stdArr[i].age);
		}
		System.out.println("============");
		
		// 以大根堆的結構彈出
		PriorityQueue<Student> heap = new PriorityQueue<> (new studentComp());
		heap.add(std1);
		heap.add(std2);
		heap.add(std3);
		heap.add(std4);
		
		while (!heap.isEmpty()) {
			Student curStd = heap.poll();
			System.out.println(curStd.name + " " + curStd.id + " " + curStd.age);
		}
	}
	
	public static class studentComp implements Comparator<Student> {
		public int compare (Student std1, Student std2) {
			return std2.age - std1.age;
		}
	}
}
 

3.2 桶排序思想下的具體排序：計數排序、基數排序