2D arrays

   //  TRANSPOSE OF A MATRIX 
   import java.util.*;
public class Main
{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();                                     //  3
		int a[][] = new int[n][n];                               //   1 2 3
		for(int i=0;i<n;i++){                                    //   4 5 6
		    for(int j=0;j<n;j++){                                //   7 8 9
		        a[i][j]=sc.nextInt();
		    }
		}
		//extra space
// 		for(int i=0;i<n;i++){
// 		    for(int j=0;j<n;j++){
// 		        System.out.print(a[j][i] + " ");
// 		    }
// 		    System.out.println();
// 		}
        
        // by using swapping Method(no extra space is required)            //  1 4 7
         for(int i=0;i<n;i++){                                             //  2 5 8 
             for(int j=i+1;j<n;j++){                                       //  3 6 9
                 
                 int temp = a[i][j];
                 a[i][j] = a[j][i];
                 a[j][i] =temp; 
                 
             }
         }
         
        // ROTATE A MATIRX BY 90 DEGREE CLOCKWISE
          for(int i=0;i<n;i++){
         int start =0;
         int end = n-1;
         while(start<end){
             int temp =a[i][start];  //coulmn changes
             a[i][start]=a[i][end];
             a[i][end] =temp;
             start++;
             end--;
         }
    }
         for(int  i=0;i<n;i++){
             for(int j=0;j<n;j++){                                            // 7 4 1
                 System.out.print(a[i][j] + " ");                            //  8 5 2
             }                                                               //  9 6 3
                      System.out.println();
         }

	}
}


/*    You are given a chessboard of size N x N, where the top left square is black. Each square contains a value. 
Find the sum of values of all black square and all white squares                          */
import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
	   Scanner sc = new Scanner(System.in);
      int n =sc.nextInt();
      int a[][] = new int[n][n];
      for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
          a[i][j] =sc.nextInt();
        }
      }
      int sum_black =0;
      int sum_white =0;
      for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
          if((i+j)%2==0){
            sum_black += a[i][j];
          }
          else{
            sum_white +=a[i][j];
          }
        }
      }
      System.out.println(sum_black);
      System.out.println(sum_white);
      
	}
}

         /* Given a 2D array, the task is to print the 2D in alternate manner (First row from left to right, then from right to left, and so on).
         Examples:  Input : arr[][2] = [[1, 2], [2, 3]]; Output : 1 2 3 2        */
         
         import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner sc =new Scanner(System.in);
      int m =sc.nextInt();
      int n =sc.nextInt();
      int a[][]= new int[m][n];
      for(int i=0;i<m;i++){
        for(int j=0;j<n;j++){
          a[i][j] =sc.nextInt();
        }
      }

      for(int i=0;i<m;i++){
       for(int j=0;j<n;j++){
          if(i%2==0){
            System.out.print(a[i][j]+" ");
          }
          else{
            System.out.print(a[i][n-j-1]+" ");
          }
       }
        }  
	}
}


// SPIRALLY TRAVERSING THE MATRIX
import java.util.*;
import java.lang.*;
import java.io.*;

public class Main
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner sc = new Scanner(System.in);
      int m =sc.nextInt();                           // 3 3
      int n = sc.nextInt();                          // 1 2 3
      int a[][]= new int[m][n];                      // 4 5 6
      for(int i=0;i<m;i++){                          // 7 8 9 
        for(int j=0;j<n;j++){
          a[i][j] =sc.nextInt();
        }
      }
    
      int left = 0;
      int right = n-1;
      int top =0;
      int bottom =m-1;
      int dir =0;
      while(top<=bottom && left<=right){
        if(dir==0){
          for(int i =left;i<=right;i++){
            System.out.print(a[top][i]+" ");
          }
          top++;
          dir=1;
        }
        
       else  if(dir==1){
          for(int i=top;i<=bottom;i++){
            System.out.print(a[i][right]+" ");                        // 1 2 3 6 9 8 7 4 5
          }
          right--;
          dir =2;
        }
        
        else if(dir==2){
          for(int i=right;i>=left;i--){
            System.out.print(a[bottom][i]+" ");
          }
          bottom--;
          dir =3;
        }
        
       else if(dir==3){
          for(int i=bottom;i>=top;i--){
            System.out.print(a[i][left]+" ");
          }
          left++;
          dir=0;
        }
      }
      
      
        
      
      
	}
}