/**
 * 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:
    void flatten(TreeNode* root) {
        while(root){
            if(root->left && root->right){
                TreeNode* t = root->left;
                while(t->right)
                    t = t->right;
                t->right=root->right;
            }
            if(root->left){
                root->right = root->left;
                root->left=NULL;
            }
                
            root = root->right;
            
        }   
        
        
    }
};