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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 (50.22%)
* Total Accepted: 306K
* Total Submissions: 609K
* 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.
*/
#include <vector>
#include <stack>
using namespace std;
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;
if (root)
st.push(root);
while (!st.empty())
{
TreeNode *node = st.top();
st.pop();
result.push_back(node->val);
if (node->right)
st.push(node->right);
if (node->left)
st.push(node->left);
}
return result;
}
};