solve number of islands

coding_interviews/leetcode/medium/number-of-islands/number-of-islands.js

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+function isInsideTheGrid(grid, row, col) {
+  return row >= 0 && row < grid.length && col >= 0 && col < grid[0].length;
+}
+
+function dfs(grid, row, col) {
+  if (isInsideTheGrid(grid, row, col) && grid[row][col] === '1') {
+    grid[row][col] = 0; // marked as visited
+    dfs(grid, row - 1, col); // top
+    dfs(grid, row + 1, col); // bottom
+    dfs(grid, row, col - 1); // left
+    dfs(grid, row, col + 1); // right
+  }
+}
+
+function numIslands(grid) {
+  let numberOfIslands = 0;
+
+  for (let row = 0; row < grid.length; row++) {
+    for (let col = 0; col < grid[row].length; col++) {
+      if (grid[row][col] === '1') {
+        numberOfIslands++;
+        grid[row][col] = 0; // marked as visited
+
+        dfs(grid, row - 1, col); // top
+        dfs(grid, row + 1, col); // bottom
+        dfs(grid, row, col - 1); // left
+        dfs(grid, row, col + 1); // right
+      }
+    }
+  }
+
+  return numberOfIslands;
+}