1using System;
2using System.Collections.Generic;
3using System.Linq;
4
5public class Solution {
6    public IList<int> LuckyNumbers (int[][] matrix) {
7        List<int> result = new List<int>();
8        int m = matrix.Length;
9        int n = matrix[0].Length;
10        int[] minRow = new int[m];
11
12        for (int i = 0; i < m; i++) {
13            minRow[i] = int.MaxValue;
14            for (int j = 0; j < n; j++) {
15                minRow[i] = Math.Min(minRow[i], matrix[i][j]);
16            }
17        }
18
19        for (int j = 0; j < n; j++) {
20            int maxCol = int.MinValue;
21            for (int i = 0; i < m; i++) {
22                maxCol = Math.Max(maxCol, matrix[i][j]);
23            }
24            for (int i = 0; i < m; i++) {
25                if (matrix[i][j] == maxCol && matrix[i][j] == minRow[i]) {
26                    result.Add(matrix[i][j]);
27                }
28            }
29        }
30        return result;
31    }
32}

1using System.Collections.Generic;
using System.Linq;

public class Solution {
    public IList<int> LuckyNumbersWithSet(int[][] matrix) {
        HashSet<int> rowMinSet = new HashSet<int>();
        foreach (var row in matrix) {
            rowMinSet.Add(row.Min());
        }

        int[] colMax = new int[matrix[0].Length];
        Array.Fill(colMax, int.MinValue);

        for (int j = 0; j < matrix[0].Length; j++) {
            for (int i = 0; i < matrix.Length; i++) {
                colMax[j] = Math.Max(colMax[j], matrix[i][j]);
            }
        }

        List<int> luckyNumbers = new List<int>();
        foreach (int max in colMax) {
            if (rowMinSet.Contains(max)) {
                luckyNumbers.Add(max);
            }
        }

        return luckyNumbers;
    }
}