【练习二】数组相关练习

10：定义一个4行4列的二维数组，逐个从键盘输入值，将对角线的值清0

public class DemoTest1 {

	public static void main(String[] args) {

		int[][] arr = new int[4][4];
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++) {
				arr[i][j]=(int)(Math.random()*(55-20)+20);
			}
		}
		
		System.out.println("原数组：");
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++) {
				System.out.print(arr[i][j]+"\t");
			}
			System.out.println();
		}
		for (int i = 0; i < arr.length; i++) {
				arr[i][i]=0;
			
		}
		System.out.println("更改后的数组：");
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++) {
				System.out.print(arr[i][j]+"\t");
			}
			System.out.println();
		}
	}
}

 11：定义一个N*N二维数组，从键盘上输入值，找出每行中最大值组成一个一维数组并输出；

import java.util.Scanner;

public class DemoTest2 {

	public static void main(String[] args) {

		Scanner sc = new Scanner(System.in);
		System.out.println("请输入数组的边长：");
		int num = sc.nextInt();
		int[][] arr = new int[num][num];
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++) {
				arr[i][j]=(int)(Math.random()*(55-20)+20);
			}
		}
		System.out.println("原数组：");
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr.length; j++) {
				System.out.print(arr[i][j]+"\t");
			}
			System.out.println();
		}
		
		int max;
		int[] arr1 = new int[num];
		for (int i = 0; i < arr.length; i++) {
			max = arr[i][0];
			for (int j = 0; j < arr1.length; j++) {
				if(max<= arr[i][j]){
					max=arr[i][j];
				}
			}
			arr1[i]=max;
		}
		System.out.println("最大数组成的数组：");
		for(int i : arr1){
			System.out.print(i+"\t");
	
		}
	}
}

12：从键盘上输入一个 3*4 的整型数组，求出其中的最大值和最小值，并显示出

package Arraysexer1;

public class DemoTest3 {

	public static void main(String[] args) {

		int[][] arr = new int[3][4];
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr[i].length; j++) {
				arr[i][j]=(int)(Math.random()*(55-20)+20);
			}
		}
		System.out.println("原数组：");
		for (int i = 0; i < arr.length; i++) {
			for (int j = 0; j < arr[i].length; j++) {
				System.out.print(arr[i][j]+"\t");
			}
			System.out.println();
		}
		int max = 0;
		int min = 0;
		for (int i = 0; i < arr.length; i++) {
			max = arr[i][0];
			min = arr[i][0];
			for (int j = 0; j < arr.length; j++) {
				if(max<=arr[i][j]){
					max=arr[i][j];
				}
				if(min>=arr[i][j]){
					min = arr[i][j];
				}
			}
		}
		System.out.println("最大值："+max);
		System.out.println("最小值："+min);
	}
}

13：有10个数字要求分别用选择法和冒泡法从大到小输出

public class DemoTest4 {

   public static void main(String[] args) {

//   有10个数字要求分别用选择法和冒泡法从大到小输出

     int[] arr = {10,9,8,7,6,5,4,3,2,1};

     for (int i = 0; i < arr.length-1; i++) {

        for (int j = 0; j < arr.length-1-i; j++) {

           if(arr[j]<arr[j+1]){

             int x=arr[j];

             arr[j]=arr[j+1];

             arr[j+1]=x;

           }

        }

     }

     System.out.println("排序为：");

     for(int i:arr){

        System.out.print(+i+"\t");

     }

    

//   选择排序

     int max=0;

     for(int i=0;i<arr.length;i++){

        max=arr[i];

        for(int j=i;j<arr.length-1;j++){

           if(max<arr[j+1]){

             max=arr[i];

           }

        }

        int x=arr[i];

        arr[i]=max;

        max=x;

     }

     System.out.println();

     System.out.println("排序为：");

     for(int i:arr){

        System.out.print(+i+"\t");

     }

   }

}