solves lucky numbers in a matrix

Author: anishLearnsToCode

README.md

@@ -351,7 +351,7 @@
 | 1365 | [How Many Numbers Are Smaller Than Current Number](https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number)               |                                                    [![Java](assets/java.png)](src/HowManyNumbersAreSmallerThanCurrentNumber.java)                                                    |                                                                                                                                   |
 | 1370 | [Increasing Decreasing String](https://leetcode.com/problems/increasing-decreasing-string)                                                           |                                                           [![Java](assets/java.png)](src/IncreasingDecreasingString.java)                                                            |                                                                                                                                   |
 | 1374 | [Generate A String With Characters That Have Odd Count](https://leetcode.com/problems/generate-a-string-with-characters-that-have-odd-counts)        |                                                 [![Java](assets/java.png)](src/GenerateAStringWithCharactersThatHaveOddCounts.java)                                                  |                                                                                                                                   |
-| 1380 | [Lucky Numbers In A Matrix](https://leetcode.com/problems/lucky-numbers-in-a-matrix)                                                                 |                                                                                                                                                                                      |                                                                                                                                   |
+| 1380 | [Lucky Numbers In A Matrix](https://leetcode.com/problems/lucky-numbers-in-a-matrix)                                                                 |                                                              [![Java](assets/java.png)](src/LuckyNumbersInAMatrix.java)                                                              |                                                                                                                                   |
 | 1385 | [Find The Distance Value Between 2 Arrays](https://leetcode.com/problems/find-the-distance-value-between-two-arrays)                                 |                                                                                                                                                                                      |                                                                                                                                   |
 | 1389 | [Create Target Array in Given Order](https://leetcode.com/problems/create-target-array-in-the-given-order)                                           |                                                                                                                                                                                      |                                                                                                                                   |
 | 1394 | [Find Lucky Integer In An Array](https://leetcode.com/problems/find-lucky-integer-in-an-array)                                                       |                                                                                                                                                                                      |                                                                                                                                   |

src/LuckyNumbersInAMatrix.java

@@ -0,0 +1,49 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class LuckyNumbersInAMatrix {
+    public List<Integer> luckyNumbers (int[][] matrix) {
+        final int rows = matrix.length, columns = matrix[0].length;
+        final List<Integer> luckyNumbers = new ArrayList<>();
+        int[] columnMax = getMaxOfColumns(matrix);
+        for (int row = 0 ; row < rows ; row++) {
+            RowMin rowMin = RowMin.from(matrix[row]);
+            if (rowMin.min == columnMax[rowMin.index]) {
+                luckyNumbers.add(rowMin.min);
+            }
+        }
+        return luckyNumbers;
+    }
+
+    private static final class RowMin {
+        private final int index;
+        private final int min;
+
+        private RowMin(int index, int min) {
+            this.index = index;
+            this.min = min;
+        }
+
+        private static RowMin from(int[] row) {
+            int minIndex = 0, min = row[0];
+            for (int i = 1; i < row.length; i++) {
+                if (row[i] < min) {
+                    minIndex = i;
+                    min = row[i];
+                }
+            }
+            return new RowMin(minIndex, min);
+        }
+    }
+
+    private int[] getMaxOfColumns(int[][] grid) {
+        final int rows = grid.length, columns = grid[0].length;
+        final int[] columnsMax = new int[columns];
+        for (int[] row : grid) {
+            for (int column = 0 ; column < columns ; column++) {
+                columnsMax[column] = Math.max(columnsMax[column], row[column]);
+            }
+        }
+        return columnsMax;
+    }
+}