Add number-of-islands solution

Author: Jeehay28

number-of-islands/Jeehay28.js

@@ -0,0 +1,50 @@
+/**
+ * @param {character[][]} grid
+ * @return {number}
+ */
+
+// 🌻
+// Time Complexity: O(m * n), where M is the number of rows and N is the number of columns in the grid.
+// Space Complexity: O(k), where k is the size of the largest island (k <= m * n)
+
+// The space complexity is determined by the depth of the recursive stack used by the sink function.
+// In the worst-case scenario, where the entire grid is filled with "1"s (a single large island),
+// the depth of recursion could go up to O(m * n).
+
+var numIslands = function (grid) {
+  // depth-first search (DFS) that potentially visits every connected cell in the current island
+  const sink = (row, col) => {
+    grid[row][col] = "0";
+
+    const adjacent = [
+      [row - 1, col], // up
+      [row + 1, col], // down
+      [row, col - 1], // left
+      [row, col + 1], // right
+    ];
+
+    for ([r, c] of adjacent) {
+      if (r >= 0 && r < grid.length && c >= 0 && c < grid[r].length) {
+        if (grid[r][c] === "1") {
+          sink(r, c);
+        }
+      }
+    }
+  };
+
+  let cnt = 0;
+
+  for (let i = 0; i < grid.length; i++) {
+    for (let j = 0; j < grid[0].length; j++) {
+      if (grid[i][j] === "1") {
+        cnt += 1;
+        sink(i, j);
+      }
+    }
+  }
+
+  return cnt;
+};
+
+
+