Experiment 4 array

                              Experiment four ： Array

The experiment purpose

1. Master array declaration 、 Definition 、 Initialize and use .

2. Master the access method of one-dimensional or two-dimensional array elements .

Experimental content

1. Programming , Complete the following functions ：

（1） Input 20 An integer into the array ;

（2） Yes 20 The number is sorted from large to small , Output sorted array ;

（3） Enter an integer x;

（4） Look for... In an array x. If output is found x Subscript in array , Output not found -1.

package code41;

import java.util.Scanner;

import java.util.Arrays;  // Import Arrays class

public class code41 {

public static void main(String[] args) {

// TODO Automatically generated method stubs

Scanner in = new Scanner(System.in);

int []numbers=new int[20];

System.out.println(" Please enter 20 It's an integer :");

for(int i=0;i<20;i++) {

numbers[i]=in.nextInt();  // adopt nextInt Method to read the number entered by the user in turn and store it in the array

}

Arrays.sort(numbers);  // take 20 An integer is sorted from small to large

for(int i = 19;i>=0;i--) {

System.out.println(numbers[i]);  // Output in reverse order , That is, convert it to sort from large to small

}

System.out.println(" Please enter an integer x:");

int x=in.nextInt(),j=0;

for(int i=0;i<20;i++) {

if(x==numbers[i])  // Look for... In an array x

{

System.out.println(i);  // Output x Subscript in array

j=1;

}

}

if(j!=1)

{

System.out.println("-1");  // Output if you can't find it -1

}

}

}

1. Output a stored in a two-dimensional array 3*3 matrix , And find the sum of diagonal elements .

package code42;

import java.util.Scanner;

public class code42 {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

int numbers[][]=new int[3][3];  // Define this array and allocate memory space to it

int i,j,sum=0;

System.out.println(" Please enter 3*3 The elements of a matrix ：");

Scanner in = new Scanner(System.in);

for(i=0;i<3;i++) {

for(j=0;j<3;j++) {

numbers[i][j]=in.nextInt();  // Input array elements

if(i==j)  // Determine whether it is a diagonal element

{

sum+=numbers[i][j];  // Sum up

}

}

}

System.out.println(" The sum of diagonal elements is :"+sum);

System.out.println(" Output 3*3 Array of :");

for(i=0;i<3;i++) {

for(j=0;j<3;j++) {

System.out.print(" "+numbers[i][j]);  // Output two-dimensional array

}

System.out.println();

}

}

}

3. Print Yang Hui triangle in the following form  

               1

               1   1

               1   2   1

               1   3   3   1

               1   4   6   4   1

               1   5   10  10  5   1

   ........................

     Before output 10 That's ok .

package code43;

public class code43 {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

int[][]num=new int[10][10];  // Define a Yang Hui triangle with ten rows and ten columns

for(int i=0;i<num.length;i++) {

for(int j=0;j<num.length;j++) {

num[i][0]=1;

num[i][j]=1;  // The first and last columns of each row are 1

}

}

for(int i=2;i<num.length;i++) {

for(int j=1;j<i;j++) {

num[i][j]=num[i-1][j]+num[i-1][j-1];  // Each number is equal to the sum of the two numbers above it

}

}

for(int i=0;i<num.length;i++) {

for(int j=0;j<=i;j++) {

System.out.print(num[i][j]+" ");  // Output Yang Hui triangle

}

System.out.println();

}

}

}

4. Yes M A circle of individuals , Each person has a number （1.2.3.....M）, Count from the first person , To report for duty N This person is out of the circle . Continue counting , Count to N At that time, this man made a circle again . Until there's only one left , Output the order of the circle .M、N Input from keyboard .

package code44;

import java.util.Scanner;

public class code44 {

public static void main(String[] args) {

// TODO  Automatically generated method stubs

Scanner in=new Scanner(System.in);

System.out.println(" Please enter the total number of people ：");

int M=in.nextInt();

System.out.println(" This person will leave the circle as soon as he reports for duty ：");

int N=in.nextInt();

int num[]=new int[M];

int a=M,b=-1,c=0;

for(int i=0;i<M;i++) {

c++;

num[i]=c;  // Number the array

}

System.out.println(" Original sort :");

for(int i=0;i<M;i++) {

System.out.print(num[i]+"\t");

}

System.out.println();

System.out.println(" Output the order of the circle ：");

while(a!=1) {  // End of control cycle

for(int i=0;i<N;i++) {

b++;

if(b==M)

{

b=0;  // Count

}

if(num[b]==0)

{

i--;  // Prevent double counting

}

}

if(num[b]!=0)

{

System.out.print(num[b]+"\t");  // The sorting number of the output number

num[b]=0;  // Exclude the selected number

}

a--;

}

}

}

Summary of experiments

1. When defining an array , Except to give the name of the array 、 Member type , Also allocate memory space for it , And initialize ;
2. When defining an array , Do not allow the [] Specify the number of array elements in ;
3. Arrays cannot be assigned as a whole ;
4. Import Arrays class , Use Arrays.sort() Method can sort the elements in the specified array from small to large ;
5. Java Some examples of array experiment problems, such as matrix 、 Yang hui triangle 、 Joseph Ring problem has its fixed Algorithm .