94、Binary Tree Inorder Traversal

题目：

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?
解题思路：
迭代法中序遍历。

python版本：

class Solution(object):
def inorderTraversal(self, root):
"""
:type root: TreeNode
:rtype: List[int]
"""
def goAlongLeft(x,s):
while(x):
s.append(x)
x = x.left
stack,res = [],[]
x = root
while(True):
goAlongLeft(x,stack)
if(len(stack)==0):break
x = stack.pop()
res.append(x.val)
x = x.right
return res

c++版本：

class Solution {
public:
void goAlongLeft(TreeNode *x,stack<TreeNode *>&s){
while(x){
s.push(x);
x = x->left;
}
}
vector<int> inorderTraversal(TreeNode* root) {
TreeNode *x = root;
vector<int> res;
stack<TreeNode *>s;
while(true){
goAlongLeft(x,s);
if(s.empty())break;
x = s.top();s.pop();
res.push_back(x->val);
x = x->right;
}
return res;
}
};