Add solution #1254

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,198 LeetCode solutions in JavaScript
+# 1,199 LeetCode solutions in JavaScript
 
 [https://leetcodejavascript.com](https://leetcodejavascript.com)
 
@@ -956,6 +956,7 @@
 1250|[Check If It Is a Good Array](./solutions/1250-check-if-it-is-a-good-array.js)|Hard|
 1252|[Cells with Odd Values in a Matrix](./solutions/1252-cells-with-odd-values-in-a-matrix.js)|Easy|
 1253|[Reconstruct a 2-Row Binary Matrix](./solutions/1253-reconstruct-a-2-row-binary-matrix.js)|Medium|
+1254|[Number of Closed Islands](./solutions/1254-number-of-closed-islands.js)|Medium|
 1261|[Find Elements in a Contaminated Binary Tree](./solutions/1261-find-elements-in-a-contaminated-binary-tree.js)|Medium|
 1267|[Count Servers that Communicate](./solutions/1267-count-servers-that-communicate.js)|Medium|
 1268|[Search Suggestions System](./solutions/1268-search-suggestions-system.js)|Medium|

solutions/1254-number-of-closed-islands.js

@@ -0,0 +1,57 @@
+/**
+ * 1254. Number of Closed Islands
+ * https://leetcode.com/problems/number-of-closed-islands/
+ * Difficulty: Medium
+ *
+ * Given a 2D grid consists of 0s (land) and 1s (water).  An island is a maximal 4-directionally
+ * connected group of 0s and a closed island is an island totally (all left, top, right, bottom)
+ * surrounded by 1s.
+ *
+ * Return the number of closed islands.
+ */
+
+/**
+ * @param {number[][]} grid
+ * @return {number}
+ */
+var closedIsland = function(grid) {
+  const rows = grid.length;
+  const cols = grid[0].length;
+
+  for (let i = 0; i < rows; i++) {
+    markBorderConnected(i, 0);
+    markBorderConnected(i, cols - 1);
+  }
+  for (let j = 0; j < cols; j++) {
+    markBorderConnected(0, j);
+    markBorderConnected(rows - 1, j);
+  }
+
+  let result = 0;
+  for (let i = 1; i < rows - 1; i++) {
+    for (let j = 1; j < cols - 1; j++) {
+      result += countClosed(i, j);
+    }
+  }
+
+  return result;
+
+  function markBorderConnected(row, col) {
+    if (row < 0 || row >= rows || col < 0 || col >= cols || grid[row][col] !== 0) return;
+    grid[row][col] = 1;
+    markBorderConnected(row - 1, col);
+    markBorderConnected(row + 1, col);
+    markBorderConnected(row, col - 1);
+    markBorderConnected(row, col + 1);
+  }
+
+  function countClosed(row, col) {
+    if (row < 0 || row >= rows || col < 0 || col >= cols || grid[row][col] !== 0) return 0;
+    grid[row][col] = 1;
+    countClosed(row - 1, col);
+    countClosed(row + 1, col);
+    countClosed(row, col - 1);
+    countClosed(row, col + 1);
+    return 1;
+  }
+};