feat: add typescript solution to locf problem: No.07. Build Tree (#425)

Author: zhaocchen

lcof/面试题07. 重建二叉树/README.md

@@ -187,6 +187,34 @@ private:
 };
 ```
 
+### **TypeScript**
+
+```ts
+/**
+ * Definition for a binary tree node.
+ * 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 {
+    if (preorder.length == 0) return null;
+    let val: number = preorder[0];
+    let node: TreeNode = new TreeNode(val);
+    let index: number = inorder.indexOf(val);
+    node.left = buildTree(preorder.slice(1, index + 1), inorder.slice(0, index));
+    node.right = buildTree(preorder.slice(index + 1), inorder.slice(index + 1));
+    return node;
+};
+```
+
 ### **...**
 
 ```

lcof/面试题07. 重建二叉树/Solution.ts

@@ -0,0 +1,23 @@
+/**
+ * Definition for a binary tree node.
+ * 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 {
+    if (preorder.length == 0) return null;
+    let val: number = preorder[0];
+    let node: TreeNode = new TreeNode(val);
+    let index: number = inorder.indexOf(val);
+    node.left = buildTree(preorder.slice(1, index + 1), inorder.slice(0, index));
+    node.right = buildTree(preorder.slice(index + 1), inorder.slice(index + 1));
+    return node;
+};