solve: construct binary tree from preorder and inorder traversal

Author: tolluset

construct-binary-tree-from-preorder-and-inorder-traversal/tolluset.ts

@@ -0,0 +1,36 @@
+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(n^2)
+ *  SC: O(n)
+ * */
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+  if (!preorder?.length || !inorder?.length) {
+    return null;
+  }
+
+  const rootValue = preorder[0];
+  const root = new TreeNode(rootValue);
+  const inorderRootIndex = inorder.indexOf(rootValue);
+
+  root.left = buildTree(
+    preorder.slice(1, inorderRootIndex + 1),
+    inorder.slice(0, inorderRootIndex),
+  );
+
+  root.right = buildTree(
+    preorder.slice(inorderRootIndex + 1),
+    inorder.slice(inorderRootIndex + 1),
+  );
+
+  return root;
+}