java: add «1380. Lucky Numbers in a Matrix»

Signed-off-by: Matej Focko <me@mfocko.xyz>

java/lucky-numbers-in-a-matrix.java

@@ -0,0 +1,29 @@
+class Solution {
+  public List<Integer> luckyNumbers(int[][] matrix) {
+    int rows = matrix.length, cols = matrix[0].length;
+
+    int rowCandidate = Integer.MIN_VALUE;
+    for (int y = 0; y < rows; ++y) {
+      int currentRow = matrix[y][0];
+      for (int x = 1; x < cols; ++x) {
+        currentRow = Math.min(currentRow, matrix[y][x]);
+      }
+      rowCandidate = Math.max(rowCandidate, currentRow);
+    }
+
+    int colCandidate = Integer.MAX_VALUE;
+    for (int x = 0; x < cols; ++x) {
+      int currentCol = matrix[0][x];
+      for (int y = 1; y < rows; ++y) {
+        currentCol = Math.max(currentCol, matrix[y][x]);
+      }
+      colCandidate = Math.min(colCandidate, currentCol);
+    }
+
+    if (rowCandidate == colCandidate) {
+      return Arrays.asList(rowCandidate);
+    }
+
+    return List.<Integer>of();
+  }
+}