Add subtree-of-another-tree solution in TS

Author: Jeehay28

subtree-of-another-tree/Jeehay28.ts

@@ -0,0 +1,29 @@
+class TreeNode {
+  val: number;
+  left: TreeNode | null;
+  right: TreeNode | null;
+  constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+    this.val = val === undefined ? 0 : val;
+    this.left = left === undefined ? null : left;
+    this.right = right === undefined ? null : right;
+  }
+}
+
+// TC: O(m + n), m = number of nodes in root, n = number of nodes in subRoot
+// SC: O(m + n)
+function isSubtree(root: TreeNode | null, subRoot: TreeNode | null): boolean {
+  const serializeNode = (node: TreeNode | null) => {
+    if (!node) return "$";
+
+    const str = `(${node.val},${serializeNode(node.left)},${serializeNode(
+      node.right
+    )})`;
+
+    return str;
+  };
+
+  const serializedRoot = serializeNode(root);
+  const serializedSubRoot = serializeNode(subRoot);
+
+  return serializedRoot.includes(serializedSubRoot);
+}