Flatten Binary Tree to Linked List.txt

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    void flatten(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        TreeNode* last = NULL;
        flattenN(root, last);
    }
    void flattenN(TreeNode* root, TreeNode*& last) {
        if (root == NULL)
            return;
        flattenN(root->right, last);
        flattenN(root->left, last);
        root->right = last;
        root->left = NULL;
        last = root;
    }
};