15.py

# Write a function solve that rotates an n x n matrix 90 degrees clockwise in-place.

def solve(matrix):
    for i in range(int(len(matrix))):
        for j in range(i):
            matrix[i][j], matrix[j][i] = matrix[j][i], matrix[i][j]
    for list in matrix:
        list.reverse()
    return matrix