2.1.16

question:

Certification. Write a check() method that call sort() for a given array and returns true if sort() puts the array in order and leaves the same set of objects in the array as were there initially, false otherwise. Do

answer:

//判断长度是否相等，排序是否正确，排序前数组每个元素的个数与在排序后数组中该元素个数是否相等

import edu.princeton.cs.algs4.*;
import java.util.Arrays;

public class Certification
{   
    public static boolean check(Comparable[] a)
    {
        Comparable[] b = new Comparable[a.length];
        System.arraycopy(a,0,b,0,a.length);//复制数组
        Arrays.sort(a);
        //a[0] = 10.0;用于判断
        for(int i = 1; i < a.length; i++)//排序正确性检测
        {
            if(a[i].compareTo(a[i-1])<0)
                return false;
        }
        if(a.length != b.length)//长度检测
            return false;
        for(int i = 0; i < b.length; i++)
        {
            int num1 = 0;
            int num2 = 0;
            for(int j = 0; j < b.length; j++)//计算原数组中与第i个元素相同的个数
            {
                if(b[j]==b[i])
                    num1++;
            }
            for(int j = 0; j < a.length; j++)//计算排序后数组中与第i个元素相同的个数
            {
                if(a[j]==b[i])
                    num2++;
            }
            if(num1 != num2)
                return false;
        }
        return true;
    }
    
    public static void main(String[] args)
    {
        String[] a = In.readStrings();
        if(check(a) == true)
            StdOut.println("no problem");
        else
            StdOut.println("wrong");
    }
}