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flaatenbst.cpp
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flaatenbst.cpp
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/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
void flatten(TreeNode* root) {
if(!root)return;
stack<TreeNode*>s;
s.push(root);
while(!s.empty()){
TreeNode* cur = s.top();
s.pop();
if(cur->right)s.push(cur->right);
if(cur->left)s.push(cur->left);
if(!s.empty()){
cur->right = s.top();
}
cur->left = nullptr;
}
}
};