【leetcode】1380. Lucky Numbers in a Matrix

题目如下：

Given a m * 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]

Constraints:

• m == mat.length
• n == mat[i].length
• 1 <= n, m <= 50
• 1 <= matrix[i][j] <= 10^5.
• All elements in the matrix are distinct.

解题思路：把每一行的最小值和每一列的最大值算出来即可。

代码如下：

class Solution(object):
    def luckyNumbers (self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        row_min = [float('inf')] *  len(matrix)
        column_max = [-float('inf')] * len(matrix[0])

        for i in range(len(matrix)):
            for j in range(len(matrix[i])):
                row_min[i] = min(row_min[i],matrix[i][j])
                column_max[j] = max(column_max[j],matrix[i][j])
        res = []
        for i in range(len(matrix)):
            for j in range(len(matrix[i])):
                if matrix[i][j] == row_min[i] == column_max[j]:
                    res.append(matrix[i][j])

        return res