1380. Lucky Numbers in a Matrix

Description

Given an m x n matrix of distinct numbers, return all lucky numbers in the matrix in any order.

A lucky number is an element of the matrix such that it is the minimum element in its row and maximum in its column.

Example 1:

Input: matrix = [[3,7,8],[9,11,13],[15,16,17]]
Output: [15]
Explanation: 15 is the only lucky number since it is the minimum in its row and the maximum in its column.

Example 2:

Input: matrix = [[1,10,4,2],[9,3,8,7],[15,16,17,12]]
Output: [12]
Explanation: 12 is the only lucky number since it is the minimum in its row and the maximum in its column.

Example 3:

Input: matrix = [[7,8],[1,2]]
Output: [7]
Explanation: 7 is the only lucky number since it is the minimum in its row and the maximum in its column.

Constraints:

m == mat.length
n == mat[i].length
1 <= n, m <= 50
1 <= matrix[i][j] <= 10⁵.
All elements in the matrix are distinct.

Solution

lucky-numbers-in-a-matrix.py

class Solution:
    def luckyNumbers (self, matrix: List[List[int]]) -> List[int]:
        r,c = len(matrix), len(matrix[0])
        col = [0] * c
        # calculate max col
        for i in range(c):
            col[i] = max([matrix[j][i] for j in range(r)])

        res = []
        for i in range(r):
            for j in range(c):
                if min(matrix[i]) == matrix[i][j] and col[j] == matrix[i][j]:
                    res.append(matrix[i][j])

        return res