Add solution #1020

Author: JoshCrozier

README.md

@@ -1,4 +1,4 @@
-# 1,094 LeetCode solutions in JavaScript
+# 1,095 LeetCode solutions in JavaScript
 
 [https://leetcode.com/](https://leetcode.com/)
 
@@ -828,6 +828,7 @@
 1017|[Convert to Base -2](./solutions/1017-convert-to-base-2.js)|Medium|
 1018|[Binary Prefix Divisible By 5](./solutions/1018-binary-prefix-divisible-by-5.js)|Easy|
 1019|[Next Greater Node In Linked List](./solutions/1019-next-greater-node-in-linked-list.js)|Medium|
+1020|[Number of Enclaves](./solutions/1020-number-of-enclaves.js)|Medium|
 1022|[Sum of Root To Leaf Binary Numbers](./solutions/1022-sum-of-root-to-leaf-binary-numbers.js)|Easy|
 1023|[Camelcase Matching](./solutions/1023-camelcase-matching.js)|Medium|
 1028|[Recover a Tree From Preorder Traversal](./solutions/1028-recover-a-tree-from-preorder-traversal.js)|Hard|

solutions/1020-number-of-enclaves.js

@@ -0,0 +1,51 @@
+/**
+ * 1020. Number of Enclaves
+ * https://leetcode.com/problems/number-of-enclaves/
+ * Difficulty: Medium
+ *
+ * You are given an m x n binary matrix grid, where 0 represents a sea cell and 1 represents
+ * a land cell.
+ *
+ * A move consists of walking from one land cell to another adjacent (4-directionally) land cell
+ * or walking off the boundary of the grid.
+ *
+ * Return the number of land cells in grid for which we cannot walk off the boundary of the grid
+ * in any number of moves.
+ */
+
+/**
+ * @param {number[][]} grid
+ * @return {number}
+ */
+var numEnclaves = function(grid) {
+  const rows = grid.length;
+  const cols = grid[0].length;
+
+  for (let i = 0; i < rows; i++) {
+    exploreBoundary(i, 0);
+    exploreBoundary(i, cols - 1);
+  }
+
+  for (let j = 0; j < cols; j++) {
+    exploreBoundary(0, j);
+    exploreBoundary(rows - 1, j);
+  }
+
+  let result = 0;
+  for (let i = 0; i < rows; i++) {
+    for (let j = 0; j < cols; j++) {
+      result += grid[i][j];
+    }
+  }
+
+  return result;
+
+  function exploreBoundary(row, col) {
+    if (row < 0 || row >= rows || col < 0 || col >= cols || grid[row][col] !== 1) return;
+    grid[row][col] = 0;
+    exploreBoundary(row + 1, col);
+    exploreBoundary(row - 1, col);
+    exploreBoundary(row, col + 1);
+    exploreBoundary(row, col - 1);
+  }
+};