114-flatten-binary-tree-to-linked-list.cpp

/**
 * 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:
    TreeNode*prev=NULL ; 
    
    void flatten(TreeNode* root) {
        
        if(root==NULL){
            return ; 
        }
        flatten(root->right); 
        flatten(root->left); 
        root->right=prev; 
        root->left=NULL; 
        prev=root; 
        
        
    }
};