LeetCode 之 Binary Tree Preorder Traversal

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

For example:

Given binary tree

{1,#,2,3}

,

1
\
2
/
3

return

[1,2,3]

.

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

使用栈实现遍历，代码如下：

vector<int> preorderTraversal(TreeNode* root) {
stack<TreeNode*> tree;
vector<int> ans;
if(!root) return ans;
tree.push(root);
while(tree.size()){
TreeNode* temp=tree.top();
ans.push_back(temp->val);
tree.pop();
if(temp->right)
tree.push(temp->right);
if(temp->left)
tree.push(temp->left);
}
return ans;
}