867. Transpose Matrix

EasyLeetCode

Given a 2D integer array matrix, return the transpose of matrix.

The transpose of a matrix is the matrix flipped over its main diagonal, switching the matrix's row and column indices.

Example 1:

Input: matrix = [[1,2,3],[4,5,6],[7,8,9]] Output: [[1,4,7],[2,5,8],[3,6,9]]

Example 2:

Input: matrix = [[1,2,3],[4,5,6]] Output: [[1,4],[2,5],[3,6]]

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 1000
• 1 <= m * n <= 10^5
• 1 <= matrix[i][j] <= 10^4

How to solve the problem

• Using nested loop to change row and column.

Code

class Solution:
    def transpose(self, matrix: List[List[int]]) -> List[List[int]]:
        result = [[0] * len(matrix) for _ in range(len(matrix[0]))] #both work
        # result = [[0 for _ in range(len(matrix))] for _ in range(len(matrix[0]))] # both work
        for i in range(len(matrix)):
            for j in range(len(matrix[0])):
                result[j][i] = matrix[i][j]
        return result

Complexity

Time complexity: O(m*n)

• Outer loop runs m times, inner loop runs n times. So T(n) = O(m*n).

Space complexity: O(m*n)

• Create a new matrix result which space is O(m*n)