第一题没想到n4都能过

package kedaxunfei;

import java.util.Scanner;

public class bishi01 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
          Scanner scanner=new Scanner(System.in);
              int m=scanner.nextInt();
              int n=scanner.nextInt();
              int nums[][]=new int[m][n];
              for (int i=0;i<m; i++) 
                  for(int j=0;j<n;j++)
                      nums[i][j]=scanner.nextInt();
               int max=0;
               for(int i=0;i<nums.length;i++)
               {
                   for(int j=0;j<nums[0].length;j++)
                   {

                    int first=nums[i][j];
                      for(int k=0;k<m;k++)
                      {
                          for(int l=0;l<n;l++)
                          {
                              if(k==i || l==j) continue;
                              else {
                                int tem=first*nums[k][l];
                                max=Math.max(tem, max);
                            }

                          }
                      }

                   }
               }
               System.out.println(max);



        }

}

第二题我直接用了自带的排序

package kedaxunfei;

import java.util.Arrays;
import java.util.Scanner;

public class bishi02 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner scanner=new Scanner(System.in);
        int n=scanner.nextInt();
        int nums[]=new int[n];
        for(int i=0;i<n;i++)
        {
            nums[i]=scanner.nextInt();
        }
         Arrays.sort(nums);
         for(int i=0;i<n;i++)
             System.out.print(nums[i]+" ");
    }

}

第三题用bigInteger的bitcount函数就可

package kedaxunfei;

import java.math.BigInteger;
import java.util.Scanner;

public class bishi03 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
       Scanner scanner=new Scanner(System.in);
       long n=scanner.nextLong();
       BigInteger bigInteger=BigInteger.valueOf(n);
       int ans=bigInteger.bitCount();
       System.out.println(ans);

    }

}

第四题注意取模，我开始因为如果长了是不变，发现取模就直接过了

package kedaxunfei;

import java.util.Scanner;

public class bishi04 {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
      Scanner scanner=new Scanner(System.in);
      String string=scanner.nextLine();
      int n=scanner.nextInt();
      n=n%string.length();
          String a1=string.substring(0,n);
          String a2=string.substring(n,string.length());
          StringBuffer anStringBuffer=new StringBuffer();
          anStringBuffer.append(a2);
          anStringBuffer.append(a1);
          System.out.println(anStringBuffer.toString());


    }

}