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Python Program to Rotate Matrix Elements

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  • Last Updated : 09 Jun, 2022

Given a matrix, clockwise rotate elements in it.

Examples:

Input
1    2    3
4    5    6
7    8    9

Output:
4    1    2
7    5    3
8    9    6

For 4*4 matrix
Input:
1    2    3    4    
5    6    7    8
9    10   11   12
13   14   15   16

Output:
5    1    2    3
9    10   6    4
13   11   7    8
14   15   16   12

The idea is to use loops similar to the program for printing a matrix in spiral form. One by one rotate all rings of elements, starting from the outermost. To rotate a ring, we need to do following. 
    1) Move elements of top row. 
    2) Move elements of last column. 
    3) Move elements of bottom row. 
    4) Move elements of first column. 
Repeat above steps for inner ring while there is an inner ring.

Below is the implementation of above idea. Thanks to Gaurav Ahirwar for suggesting below solution. 

Python




# Python program to rotate a matrix
 
# Function to rotate a matrix
def rotateMatrix(mat):
 
    if not len(mat):
        return
     
    """
        top : starting row index
        bottom : ending row index
        left : starting column index
        right : ending column index
    """
 
    top = 0
    bottom = len(mat)-1
 
    left = 0
    right = len(mat[0])-1
 
    while left < right and top < bottom:
 
        # Store the first element of next row,
        # this element will replace first element of
        # current row
        prev = mat[top+1][left]
 
        # Move elements of top row one step right
        for i in range(left, right+1):
            curr = mat[top][i]
            mat[top][i] = prev
            prev = curr
 
        top += 1
 
        # Move elements of rightmost column one step downwards
        for i in range(top, bottom+1):
            curr = mat[i][right]
            mat[i][right] = prev
            prev = curr
 
        right -= 1
 
        # Move elements of bottom row one step left
        for i in range(right, left-1, -1):
            curr = mat[bottom][i]
            mat[bottom][i] = prev
            prev = curr
 
        bottom -= 1
 
        # Move elements of leftmost column one step upwards
        for i in range(bottom, top-1, -1):
            curr = mat[i][left]
            mat[i][left] = prev
            prev = curr
 
        left += 1
 
    return mat
 
# Utility Function
def printMatrix(mat):
    for row in mat:
        print row
 
 
# Test case 1
matrix =[
            [1234 ],
            [5678 ],
            [910, 11, 12 ],
            [13, 14, 15, 16
        ]
# Test case 2
"""
matrix =[
            [1, 2, 3],
            [4, 5, 6],
            [7, 8, 9]
        ]
"""
 
matrix = rotateMatrix(matrix)
# Print modified matrix
printMatrix(matrix)

Output: 

5 1 2 3
9 10 6 4
13 11 7 8
14 15 16 12

Time Complexity: O(max(m,n) * max(m,n))
Auxiliary Space: O(m*n)

Please refer complete article on Rotate Matrix Elements for more details!


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