LeetCode: Binary Tree Preorder Traversal [144]

【题目】

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?

【题意】

非递归返回先序遍历结果

【思路】

维护一个栈即可

【代码】

/**
* Definition for binary tree
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> preorderTraversal(TreeNode *root) {
vector<int> result;
stack<TreeNode*> st;
TreeNode*node=root;
while(node){
result.push_back(node->val);
st.push(node);
node=node->left;
}
while(!st.empty()){
node=st.top()->right; st.pop();
while(node){
result.push_back(node->val);
st.push(node);
node=node->left;
}
}
return result;
}
};