[leetcodeブラシ問題シリーズ]Flatten Binary Tree to Linked List

シミュレーション問題ですが、このタイプの問題は確かに見たことがありません.またポインタを練習しました:)

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
    TreeNode * dfs(TreeNode * root){
        if(root->left != 0){
            TreeNode * last_left = dfs(root->left);
            if(root->right == 0){
                root->right = root->left;
                root->left = 0;
                return last_left;
            }else{
                TreeNode * last_right = dfs(root->right);
                last_left->right = root->right;
                root->right = root->left;
                root->left = 0;
                return last_right;
            }
        }
        if(root->right != 0)
            return dfs(root->right);
        return root;
    }
public:
    void flatten(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root == 0)
            return ;
        dfs(root);
    }
};