Merge pull request neetcode-gh#93 from anthonysim/asim/islands

Added JS 200 Number of Islands

Author: neetcode-gh

javascript/200-Number-of-Islands.js

@@ -0,0 +1,61 @@
+// Version 1
+function explore(grid, r, c, visited) {
+  const rowInbounds = 0 <= r && r < grid.length;
+  const colInbounds = 0 <= c && c < grid[0].length;
+
+  if (!rowInbounds || !colInbounds) return false;
+  if (grid[r][c] === '0') return false;
+
+  const pos = r + ',' + c;
+
+  if (visited.has(pos)) return false;
+  visited.add(pos);
+
+  explore(grid, r - 1, c, visited);
+  explore(grid, r + 1, c, visited);
+  explore(grid, r, c - 1, visited);
+  explore(grid, r, c + 1, visited);
+
+  return true;
+}
+
+var numIslands = function (grid) {
+  const visited = new Set();
+  let count = 0;
+
+  for (let r = 0; r < grid.length; r++) {
+    for (let c = 0; c < grid[0].length; c++) {
+      if (explore(grid, r, c, visited)) {
+        count += 1;
+      }
+    }
+  }
+  return count;
+};
+
+// Version 2 (Easier to understand/read)
+function dfs(grid, i, j) {
+  if (i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] === "0") {
+    return;
+  }
+
+  grid[i][j] = "0";
+  dfs(grid, i + 1, j);
+  dfs(grid, i - 1, j);
+  dfs(grid, i, j + 1);
+  dfs(grid, i, j - 1);
+}
+
+var numIslands = function (grid) {
+  let count = 0;
+
+  for (let i = 0; i < grid.length; i++) {
+    for (let j = 0; j < grid[0].length; j++) {
+      if (grid[i][j] === "1") {
+        count += 1;
+        dfs(grid, i, j);
+      }
+    }
+  }
+  return count;
+};