LeetCode之Flatten Binary Tree to Linked List

class Solution {
public:
    void flatten(TreeNode* root) {
        if(root == nullptr) return;
        flatten(root->left);
        flatten(root->right);
        if(root->left == nullptr) return;
        TreeNode *p(root->left);
        while(p->right != nullptr) p = p->right;
        p->right = root->right;
        root->right = root->left;
        root->left = nullptr;
    }
};