First, check if the total number of elements m * n is equal to r * c. If not, return the original matrix. Otherwise, flatten the matrix and then rebuild it with new dimensions.

1. m, n = len(mat), len(mat[0]).
2. If m * n != r * c, return mat.
3. Initialize res = [[0] * c for _ in range(r)].
4. Iterate through m * n elements using a single counter k:
   • Value is at mat[k // n][k % n].
   • Place it at res[k // c][k % c].
5. Return res.

• Time Complexity: O(M * N).
• Space Complexity: O(R * C) for the result.

def matrix_reshape(mat, r, c):
    m, n = len(mat), len(mat[0])
    if m * n != r * c:
        return mat
        
    res = [[0] * c for _ in range(r)]
    for k in range(m * n):
        res[k // c][k % c] = mat[k // n][k % n]
        
    return res