Leetcode 114

/**
 * 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) {
        if(!root) return;
        if(root->left) flatten(root->left);
        if(root->right) flatten(root->right);
        TreeNode* temp = root->right;
        root->right = root->left;
        root->left = NULL;
        while(root->right) root = root->right;
        root->right = temp;
    }
 
};
似懂非懂