feat: add typescript solution to lc problem: No.0145.Binary Tree Postorder Traversal

Author: zhaocchen

solution/0100-0199/0145.Binary Tree Postorder Traversal/README.md

@@ -259,6 +259,49 @@ class Solution {
 }
 ```
 
+### **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 postorderTraversal(root: TreeNode | null): number[] {
+    if (root == null) return [];
+    let stack = [];
+    let ans = [];
+    let prev = null;
+    while (root || stack.length) {
+        while (root) {
+            stack.push(root);
+            root = root.left;
+        }
+        root = stack.pop();
+        if (!root.right || root.right == prev) {
+            ans.push(root.val);
+            prev = root;
+            root = null;
+        } else {
+            stack.push(root);
+            root = root.right;
+        }
+        
+    }
+    return ans;
+};
+```
+
+
 ### **C++**
 
 ```cpp

solution/0100-0199/0145.Binary Tree Postorder Traversal/README_EN.md

@@ -269,6 +269,48 @@ class Solution {
 }
 ```
 
+### **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 postorderTraversal(root: TreeNode | null): number[] {
+    if (root == null) return [];
+    let stack = [];
+    let ans = [];
+    let prev = null;
+    while (root || stack.length) {
+        while (root) {
+            stack.push(root);
+            root = root.left;
+        }
+        root = stack.pop();
+        if (!root.right || root.right == prev) {
+            ans.push(root.val);
+            prev = root;
+            root = null;
+        } else {
+            stack.push(root);
+            root = root.right;
+        }
+        
+    }
+    return ans;
+};
+```
+
 ### **C++**
 
 ```cpp

solution/0100-0199/0145.Binary Tree Postorder Traversal/Solution.ts

@@ -0,0 +1,37 @@
+/**
+ * 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 postorderTraversal(root: TreeNode | null): number[] {
+    if (root == null) return [];
+    let stack = [];
+    let ans = [];
+    let prev = null;
+    while (root || stack.length) {
+        while (root) {
+            stack.push(root);
+            root = root.left;
+        }
+        root = stack.pop();
+        if (!root.right || root.right == prev) {
+            ans.push(root.val);
+            prev = root;
+            root = null;
+        } else {
+            stack.push(root);
+            root = root.right;
+        }
+        
+    }
+    return ans;
+};