【LeetCode】Flatten Binary Tree to Linked List

/**
 * 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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(NULL==root) return;
        flatten(root->left);
        flatten(root->right);
        if(NULL==root->left) return;
        TreeNode *tmp=root->left;
        while(tmp->right) tmp=tmp->right;
        tmp->right=root->right;
        root->right=root->left;
        root->left=NULL;
    }
};