二叉树的统一迭代法 javaScript版本

problems/二叉树的统一迭代法.md

@@ -374,6 +374,86 @@ func postorderTraversal(root *TreeNode) []int {
 }
 ```
 
+javaScript:
+
+> 前序遍历统一迭代法
+
+```js
+
+// 前序遍历：中左右
+// 压栈顺序：右左中
+
+var preorderTraversal = function(root, res = []) {
+    const stack = [];
+    if (root) stack.push(root);
+    while(stack.length) {
+        const node = stack.pop();
+        if(!node) {
+            res.push(stack.pop().val);
+            continue;
+        }
+        if (node.right) stack.push(node.right); // 右
+        if (node.left) stack.push(node.left); // 左
+        stack.push(node); // 中
+        stack.push(null);
+    };
+    return res;
+};
+
+```
+
+> 中序遍历统一迭代法
+
+```js
+
+//  中序遍历：左中右
+//  压栈顺序：右中左
+ 
+var inorderTraversal = function(root, res = []) {
+    const stack = [];
+    if (root) stack.push(root);
+    while(stack.length) {
+        const node = stack.pop();
+        if(!node) {
+            res.push(stack.pop().val);
+            continue;
+        }
+        if (node.right) stack.push(node.right); // 右
+        stack.push(node); // 中
+        stack.push(null);
+        if (node.left) stack.push(node.left); // 左
+    };
+    return res;
+};
+
+```
+
+> 后序遍历统一迭代法
+
+```js
+
+// 后续遍历：左右中
+// 压栈顺序：中右左
+ 
+var postorderTraversal = function(root, res = []) {
+    const stack = [];
+    if (root) stack.push(root);
+    while(stack.length) {
+        const node = stack.pop();
+        if(!node) {
+            res.push(stack.pop().val);
+            continue;
+        }
+        stack.push(node); // 中
+        stack.push(null);
+        if (node.right) stack.push(node.right); // 右
+        if (node.left) stack.push(node.left); // 左
+    };
+    return res;
+};
+
+```
+
 
 
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