Rotate Matrix by 90 Degrees in Java | Rotate Matrix in Java Clockwise and Anti-clockwise

In this section, we will create a Java program to rotate a matrix by 90 degrees in a clockwise and anti-clockwise rotation. The clockwise rotation is also known as the right rotation of the matrix and the anti-clockwise rotation of the matrix is also known as the left rotation of the matrix.

Rotate Matrix 90 Degree Clockwise or Right Rotation

The rotation of a matrix involves two steps:

First, find the transpose of the given matrix.
Swap the elements of the first column with the last column (if the matrix is of 3*3). The second column remains the same.

It is an efficient solution.

Note: Matrix must have the same number of rows and columns.

Let's understand through an example. Suppose, the matrix is:

Let's find the transpose of the matrix.

To get the rotated matrix, swap the first column with the last column.

The above matrix is rotated by 90 degrees.

If the given matrix is 4*4 matrix, swap the first column with the last column and the second column with the third column. For example, consider the following figure.

Step 1: Find the transpose of the matrix.

for(int i=0; i<matrix.size(); i++)
{
for(int j=i; j<matrix[i].size(); j++)
{
//checks if i is not equal to j because in transpose matrix diagonal elements will not swap
if(i!=j)
{
//swapping elements
int temp = matrix[i][j];
matrix[i][j]=marix[j][i];
matrix[j][i]=temp;
}
}
}

Step 2: Swap the elements.

for(int i=0; i<n; i++)  //n is the number of rows
{
for(int j=i; j<c/2; j++)   //c is the number of columns
{
if(i!=j)
{
//swapping elements of the first column with last column
int temp = matrix[i][j];
matrix[i][j]=marix[i][c-j-1];
matrix[i][c-j-1]=temp;
}
}
}

Let's implement the above logic in a Java program.

RotateMatrix.java

public class RotateMatrix
{
//function to rotate the matrix by 90 degrees clockwise
static void rightRotate(int matrix[][],int n)
{
//determines the transpose of the matrix
for(int i=0;i<n;i++)
{
for(int j=i;j<n;j++)
{
int temp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = temp;
}
}

//then we reverse the elements of each row
for(int i=0;i<n;i++)
{
//logic to reverse each row i.e 1D Array.  
int low = 0, high = n-1;
while(low < high)
{
int temp = matrix[i][low];
matrix[i][low] = matrix[i][high];
matrix[i][high] = temp;
low++;
high--;
}
}

System.out.println("The Right Rotated Matrix is: ");
//prints matrix after rotation
for(int i=0;i<3;i++)
{
for(int j=0;j<3;j++)
{
System.out.print(matrix[i][j]+" " +"\t");
}
System.out.println();
}
}
//driver code
public static void main(String args[])
{
int n=3;
//initializing a 3*3 matrix
int matrix[][] = new int[][]{ {1,2,3}, {4,5,6} , {7,8,9} };
System.out.println("The Original Matrix is: ");
//prints matrix
for(int i=0;i<3;i++)
{
for(int j=0;j<3;j++)
{
//prints the elements of the matrix    
System.out.print(matrix[i][j]+" " +"\t");
}
System.out.println();
}
//function calling
rightRotate(matrix, n);
}
} 

Output:

Let's see another logic for the same.

RotateMatrixClockwise.java

public class RotateMatrixClockwise
{
public static void main(String args[])
{
//matrix to rotate 
int a[][]= {{1,2,3},{4,5,6},{7,8,9}};  
System.out.println("Original Matrix: \n");
//loop for rows
for(int i=0;i<3;i++)
{
//loop for columns
for(int j=0;j<3;j++)
{
//prints the elements of the original matrix
System.out.print(" "+a[i][j]+"\t");
}
System.out.println("\n");
}
System.out.println("Rotate Matrix by 90 Degrees Clockwise: \n");
for(int i=0;i<3;i++)
{
for(int j=2;j>=0;j--)
{
//prints the elements of the rotated matrix
System.out.print(""+a[j][i]+"\t");
}
System.out.println("\n");
}
}
} 

Output:

The time complexity for the rotation of the matrix will be O(n*n) and the space complexity will be O(1) because we are not using extra space to rotate the matrix.

Rotate Matrix 90 Degree Anti-Clockwise or Left Rotation

RotateMatrix.java

public class RotateMatrix
{
//creating a function to rotate a matrix by 90 degrees Anti-clockwise
static void leftRotate(int matrix[][], int n)
{
//swapping elements of rows by columns that gives the transpose matrix
for(int i=0;i<n;i++)
{
for(int j=i;j<n;j++)
{
int temp = matrix[i][j];
matrix[i][j] = matrix[j][i];
matrix[j][i] = temp;
}
}
for(int i=0;i<n;i++)
{
//logic to swap columns
int low = 0;
int high = n-1;
while(low < high)
{
int temp = matrix[low][i];
matrix[low][i] = matrix[high][i];
matrix[high][i] = temp;
low++;
high--;
}
}
//prints the matrix elements after left rotation
System.out.println("Matrix After Left Rotation: ");
for(int i=0;i<3;i++)
{
for(int j=0;j<3;j++)
{
System.out.print(matrix[i][j]+" "+"\t");
}
System.out.println();
}
}
//driver code
public static void main(String args[])
{
//initialize number of rows and columns
int n=3;
//creating a 3*3 matrix
int matrix[][] = new int[][]{ {1,2,3}, {4,5,6} , {7,8,9} };
//prints the matrix
System.out.println("The Original Matrix is: ");
//loop for rows
for(int i=0;i<3;i++)
{
//loop for column    
for(int j=0;j<3;j++)
{
//prints elements of the matrix     
System.out.print(matrix[i][j]+" "+"\t");
}
System.out.println();
}
//function calling 
leftRotate(matrix,n);
}
}

Output:

Let's see another logic.

RotateMatrixAniclockwise.java

public class RotateMatrixAniclockwise
{
public static void main(String args[])
{
int a[][]= {{1,2,3},{4,5,6},{7,8,9}};  
System.out.println("Original Matrix: \n");
for(int i=0;i<3;i++)
{
for(int j=0;j<3;j++)
{
System.out.print(" "+a[i][j]+"\t");
}
System.out.println("\n");
}
System.out.println("Rotate Matrix by 90 Degrees Anti-clockwise: \n");
for(int i=2;i>=0;i--)
{
for(int j=0;j<=2;j++)
{
System.out.print(""+a[j][i]+"\t");
}
System.out.println("\n");
}
}
}

Output: