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144.binary-tree-preorder-traversal.cpp
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144.binary-tree-preorder-traversal.cpp
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/*
* @lc app=leetcode id=144 lang=cpp
*
* [144] Binary Tree Preorder Traversal
*
* https://leetcode.com/problems/binary-tree-preorder-traversal/description/
*
* algorithms
* Medium (52.06%)
* Likes: 855
* Dislikes: 43
* Total Accepted: 359.6K
* Total Submissions: 690.8K
* Testcase Example: '[1,null,2,3]'
*
* Given a binary tree, return the preorder traversal of its nodes' values.
*
* Example:
*
*
* Input: [1,null,2,3]
* 1
* \
* 2
* /
* 3
*
* Output: [1,2,3]
*
*
* Follow up: Recursive solution is trivial, could you do it iteratively?
*
*/
/**
* Definition for a binary tree node.
* 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> ret;
TreeNode* p = root;
stack<TreeNode*> s;
s.push(p);
while(!s.empty()) {
p = s.top();
s.pop();
if (p) {
ret.push_back(p -> val);
s.push(p -> right);
s.push(p -> left);
}
}
return ret;
}
};