add: 从前序与中序遍历序列构造二叉树

src/tree/construct-binary-tree-from-preorder-and-inorder-traversal.js

@@ -0,0 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ */
+function TreeNode (val) {
+  this.val = val
+  this.left = this.right = null
+}
+
+// 前序遍历：根左右
+// 中序遍历：左根右
+
+// 前序遍历知道根、中序遍历知道左边长度。
+
+/**
+ * @param {number[]} preorder
+ * @param {number[]} inorder
+ * @return {TreeNode}
+ */
+export const buildTree = function (preorder, inorder) {
+  if (inorder.length === 0) return null
+  const root = new TreeNode(preorder[0])
+  const index = inorder.indexOf(preorder[0])
+  root.left = buildTree(preorder.slice(1, index + 1), inorder.slice(0, index))
+  root.right = buildTree(preorder.slice(index + 1), inorder.slice(index + 1))
+  return root
+}