算法精粹(algorithm-essentials)

感谢soulmachine@github提供内容
## Binary Tree Inorder Traversal


### 描述

Given a binary tree, return the **inorder** traversal of its nodes' values.

For example:

Given binary tree `{1,#,2,3}`,

```
1
\
2
/
3
```

return `[1,3,2]`.

Note: Recursive solution is trivial, could you do it iteratively?


### 分析

用栈或者Morris遍历。


### 栈

{% if book.java %}
```java
// Binary Tree Inorder Traversal
// 使用栈,时间复杂度O(n),空间复杂度O(n)
class Solution {
public List inorderTraversal(TreeNode root) {
ArrayList result = new ArrayList<>();
Stack s = new Stack<>();
TreeNode p = root;

while (!s.empty() || p != null) {
if (p != null) {
s.push(p);
p = p.left;
} else {
p = s.pop();
result.add(p.val);
p = p.right;
}
}
return result;
}
}
```
{% endif %}

{% if book.cpp %}
```cpp
// Binary Tree Inorder Traversal
// 使用栈,时间复杂度O(n),空间复杂度O(n)
class Solution {
public:
vector inorderTraversal(TreeNode *root) {
vector result;
stack s;
const TreeNode *p = root;

while (!s.empty() || p != nullptr) {
if (p != nullptr) {
s.push(p);
p = p->left;
} else {
p = s.top();
s.pop();
result.push_back(p->val);
p = p->right;
}
}
return result;
}
};
```
{% endif %}


### Morris中序遍历

{% codesnippet "./code/binary-tree-inorder-traversal-2."+book.suffix, language=book.suffix %}{% endcodesnippet %}


### 相关题目


* [Binary Tree Preorder Traversal](binary-tree-preorder-traversal.md)
* [Binary Tree Postorder Traversal](binary-tree-postorder-traversal.md)
* [Recover Binary Search Tree](recover-binary-search-tree.md)