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+#!/usr/bin/perl
+# https://theweeklychallenge.org/blog/perl-weekly-challenge-251/#TASK2
+#
+# Task 2: Lucky Numbers
+# =====================
+#
+# You are given a m x n matrix of distinct numbers.
+#
+# Write a script to return the lucky number, if there is one, or -1 if not.
+#
+## 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
+##
+## 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
+#
+## Example 3
+##
+## Input: $matrix = [ [7 ,8],
+##                    [1 ,2] ];
+## Output: 7
+#
+############################################################
+##
+## discussion
+##
+############################################################
+#
+# For a lucky number, we know:
+# Since the minimum in a row is at the same time the maximum in
+# a column, there is no number bigger in that column, so in all
+# other rows, there is a number that is smaller than the current
+# number, so the minimum in that other row has to be smaller or
+# equal to this number; being smaller, it can't be bigger than any
+# of the numbers in the original row, so it's can't be a lucky number
+# as well.
+# So we know we have at most one lucky number.
+# Finding it is simple: In each row, find the minimum number, then
+# check whether it is as well the maximum number in its column.
+
+def lucky_numbers(matrix: list) -> None:
+    print("Input: [");
+    for row in matrix:
+        print("        [", ", ".join([str(x) for x in row]), "],")
+    print("       ];")
+    rows = len(matrix)
+    columns = len(matrix[0])
+    row_min = []
+    column_max = []
+    for column in range(columns):
+        column_elements = []
+        for row in range(rows):
+            column_elements.append(matrix[row][column])
+        column_max.append(max(column_elements))
+    for i in range(rows):
+        row_min.append(min(matrix[i]))
+        for j in range(columns):
+            elem = matrix[i][j]
+            if elem == row_min[i] and elem == column_max[j]:
+                print(f"Output: {elem}")
+                return
+    print("Output: -1")
+
+lucky_numbers([ [ 3,  7,  8], [ 9, 11, 13], [15, 16, 17] ])
+lucky_numbers([ [ 1, 10,  4,  2], [ 9,  3,  8,  7], [15, 16, 17, 12] ])
+lucky_numbers([ [7 ,8], [1 ,2] ])
+lucky_numbers([ [7 ,8], [10 ,2] ])
+