Rotate a matrix by 90 degree in clockwise direction in Java
Rotate a matrix by 90o in Java
Here, in this page we will discuss the program to rotate a matrix by 90o in Java Programming Language. We are given a row-wise sorted matrix of size r*c, we need to the rotate a matrix by 90o in clockwise direction.
Method 1 :
- First transpose the matrix.
- For this run a loop from i=0 to n and another loop from j=i+1 to j
- After doing this, now iterate over rows and reverse each rows.
- After this print the entire matrix (that gets rotated).
Time and Space Complexity :
- Time-Complexity : O(n*n)
- Space-Complexity : O(1)
Method 1 : Code in Java
Run
import java.util.*;
class Main
{
static void reverseRows (int mat[][])
{
int n = mat.length;
for (int i = 0; i < mat.length; i++){
for (int j = 0; j < mat.length/ 2; j++){
int temp = mat[i][j];
mat[i][j] = mat[i][n - j - 1];
mat[i][n - j - 1] = temp;
}
}
}
static void transpose (int arr[][])
{
for (int i = 0; i < arr.length; i++)
for (int j = i; j < arr[0].length; j++){
int temp = arr[j][i];
arr[j][i] = arr[i][j];
arr[i][j] = temp;
}
}
static void printMatrix (int arr[][]){
for (int i = 0; i < arr.length; i++){
for (int j = 0; j < arr[0].length; j++)
System.out.print (arr[i][j] + " ");
System.out.println ("");
}
}
static void rotate90 (int arr[][])
{
transpose (arr);
reverseRows (arr);
}
public static void main (String[]args)
{
int arr[][] = { {1, 2, 3, 4},
{5, 6, 7, 8},
{9, 10, 11, 12},
{13, 14, 15, 16}
};
rotate90 (arr);
printMatrix (arr);
}
}
Output :
13 9 5 1
14 10 6 2
15 11 7 3
16 12 8 4
Method 2 :
- First rotate the matrix about its main diagonal.
- For this run a loop from i=0 to n and another loop from j=0 to 1, and swap (mat[i][j], mat[j][i])
- Now, rotate the matrix about middle column.
- For this run a loop from i=0 to n, and another loop from j=0 to n/2 and swap (mat[i][j],, mat[i][n-j-1]).
- After this print the entire matrix (that gets rotated).
Time and Space Complexity :
- Time-Complexity : O(n*n)
- Space-Complexity : O(1)
Method 2 : Code in Java
Run
import java.util.*;
class Main{
public static void main(String[] args)
{
int mat[][] = { { 1, 2, 3, 4 },
{ 5, 6, 7, 8 },
{ 9, 10, 11, 12 },
{ 13, 14, 15, 16 } };
int n=4;
//Rotate the matrix about the main diagonal
for(int i=0; i<n; i++){
for(int j=0; j<i; j++){
int temp = mat[i][j];
mat[i][j] = mat[j][i];
mat[j][i] = temp;
}
}
//Rotate the matrix about middle column
for(int i=0; i<n; i++){
for(int j=0; j<n/2; j++){
int temp = mat[i][j];
mat[i][j] = mat[i][n-j-1];
mat[i][n-j-1] = temp;
}
}
for(int i=0; i<n; i++){
for(int j=0; j<n; j++){
System.out.print(mat[i][j]+" ");
}
System.out.println("");
}
}
}
Output :
13 9 5 1
14 10 6 2
15 11 7 3
16 12 8 4
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def rotateMatrix(matrix):
n = len(matrix)
# Step 1: Transpose the matrix (swap matrix[i][j] with matrix[j][i])
for i in range(n):
for j in range(i, n):
matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
# Step 2: Reverse each row
for row in matrix:
row.reverse()
# Example Usage:
matrix = [[1, 2, 3],
[4, 5, 6],
[7, 8, 9]]
rotateMatrix(matrix)
for row in matrix:
print(row)
# Output:
# [7, 4, 1]
# [8, 5, 2]
# [9, 6, 3]
a = [[5,1,9,11]
,[2,4,8,10]
,[13,3,6,7]
,[15,14,12,16] ]
result=[[0,0,0,0],
[0,0,0,0],
[0,0,0,0],
[0,0,0,0]]
for i in range(len(a)):
for j in range(len(a[0])):
result[j][i]=a[i][j]
print(result)
for i in range(len(result)):
result[i]=list(result[i])
result[i].reverse()
print(result)
import numpy as np
def rev(mat):
tr=np.transpose(mat)
ro=np.flip(tr,axis=1)
print(“roated matrix is “,ro)
original_matrix = np.array([[1, 2, 3],[4, 5, 6],[7, 8, 9]])
rev(original_matrix)