2 排序基础 - 2使用模板（泛型）编写算法

这一节我们主要在2 排序基础 - 1选择排序法
基础上增添了模板：

C++代码：

Student.h:

#ifndef INC_02_SELECTION_SORT_USING_TEMPLATE_STUDENT_H
#define INC_02_SELECTION_SORT_USING_TEMPLATE_STUDENT_H

#include 
#include 
 
using namespace std;

struct Student {

    string name;
    int score;

    // 重载小于运算法,定义Student之间的比较方式
    // 如果分数相等，则按照名字的字母序排序
    // 如果分数不等，则分数高的靠前
    bool operator<(const Student& otherStudent) {
        return score != otherStudent.score ?
            score > otherStudent.score : name < otherStudent.name;
    }

    // 重载<<符号, 定义Student实例的打印输出方式
    // * 很多同学看到这里的C++语法, 头就大了, 甚至还有同学表示要重新学习C++语言
    // * 对于这个课程, 大可不必。C++语言并不是排序重点,
    friend ostream& operator<<(ostream &os, const Student &student) {

        os << "Student: " << student.name << " " << student.score << endl;
        return os;
    }
};
#endif //INC_02_SELECTION_SORT_USING_TEMPLATE_STUDENT_H

main.cpp：

#include 
#include 
#include 
#include "Student.h"

using namespace std;

template
void selectionSort(T arr[], int n) {

    for (int i = 0; i < n; i++) {
        // 寻找[i, n)区间里的最小值
        int minIndex = i;
        for (int j = i + 1; j < n; j++)
            if (arr[j] < arr[minIndex])
                minIndex = j;

        swap(arr[i], arr[minIndex]);
    }

}

int main() {

    int a[10] = { 10,9,8,7,6,5,4,3,2,1 };
    selectionSort(a, 10);
    for (int i = 0; i < 10; i++)
        cout << a[i] << " ";
    cout << endl;

    float b[4] = {1.2,5.3,4.9,8.3};
    selectionSort(b, 4);
    for (int i = 0; i < 4; i++)
        cout << b[i] << " ";
    cout << endl;
     
    string c[4] = {"D","C","B","A"};
    selectionSort(c, 4);
    for (int i = 0; i < 4; i++)
        cout << c[i] << " ";
    cout << endl;

    Student d[4] = { {"D",90},{"C",100},{"B",95},{"A",95} };
    selectionSort(d, 4);
    for (int i  = 0; i  < 4; i ++) {
        cout << d[i];
    }
    cout << endl;
    return 0;
}

C++结果：

C++结果.png

---

java代码：

Student.java：

import java.util.*;

public class Student implements Comparable {

    private String name;
    private int score;

    public Student(String name, int score){
        this.name = name;
        this.score = score;
    }

    // 定义Student的compareTo函数
    // 如果分数相等，则按照名字的字母序排序
    // 如果分数不等，则分数高的靠前
    @Override
    public int compareTo(Student that) {

        if( this.score == that.score )
            return this.name.compareTo(that.name);

        if( this.score < that.score )
            return 1;
        else if( this.score > that.score )
            return -1;
        else // this.score == that.score
            return 0;
    }

    // 定义Student实例的打印输出方式
    @Override
    public String toString() {
        return "Student: " + this.name + " " + Integer.toString( this.score );
    }
}

SelectionSort.java：

import java.util.*;

public class SelectionSort {

    // 我们的算法类不允许产生任何实例
    private SelectionSort(){}

    public static void sort(Comparable[] arr){

        int n = arr.length;
        for( int i = 0 ; i < n ; i ++ ){
            // 寻找[i, n)区间里的最小值的索引
            int minIndex = i;
            for( int j = i + 1 ; j < n ; j ++ )
                // 使用compareTo方法比较两个Comparable对象的大小
                if( arr[j].compareTo( arr[minIndex] ) < 0 )
                    minIndex = j;

            swap( arr , i , minIndex);
        }
    }

    private static void swap(Object[] arr, int i, int j) {
        Object t = arr[i];
        arr[i] = arr[j];
        arr[j] = t;
    }

    public static void main(String[] args) {

        // 测试Integer
        Integer[] a = {10,9,8,7,6,5,4,3,2,1};
        SelectionSort.sort(a);
        for( int i = 0 ; i < a.length ; i ++ ){
            System.out.print(a[i]);
            System.out.print(' ');
        }
        System.out.println();

        // 测试Double
        Double[] b = {4.4, 3.3, 2.2, 1.1};
        SelectionSort.sort(b);
        for( int i = 0 ; i < b.length ; i ++ ){
            System.out.print(b[i]);
            System.out.print(' ');
        }
        System.out.println();

        // 测试String
        String[] c = {"D", "C", "B", "A"};
        SelectionSort.sort(c);
        for( int i = 0 ; i < c.length ; i ++ ){
            System.out.print(c[i]);
            System.out.print(' ');
        }
        System.out.println();

        // 测试自定义的类 Student
        Student[] d = new Student[4];
        d[0] = new Student("D",90);
        d[1] = new Student("C",100);
        d[2] = new Student("B",95);
        d[3] = new Student("A",95);
        SelectionSort.sort(d);
        for( int i = 0 ; i < d.length ; i ++ )
            System.out.println(d[i]);
    }
}

java结果：

java结果.png