4. construct-binary-tree-from-preorder-and-inorder-traversal

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

@@ -0,0 +1,32 @@
+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;
+  }
+}
+
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+  // build 함수가 각 노드마다 호출됨(N) * 각 노드마다 shift, indexOf 수행(N) = O(N^2)
+  function build(preorder, inorder) {
+    if (inorder.length) {
+      // TC: O(N)
+      const idx = inorder.indexOf(preorder.shift());
+      const root = new TreeNode(inorder[idx]);
+
+      root.left = build(preorder, inorder.slice(0, idx));
+      root.right = build(preorder, inorder.slice(idx + 1));
+
+      return root;
+    }
+    return null;
+  }
+
+  return build(preorder, inorder);
+}
+
+// TC: O(N^2)
+// SC: O(N^2)