[数据结构与算法]剑指 Offer 36. 二叉搜索树与双向链表 C++ 2021-08-30

剑指 Offer 36. 二叉搜索树与双向链表

中序遍历DFS void型套路

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* left;
    Node* right;

    Node() {}

    Node(int _val) {
        val = _val;
        left = NULL;
        right = NULL;
    }

    Node(int _val, Node* _left, Node* _right) {
        val = _val;
        left = _left;
        right = _right;
    }
};
*/
class Solution {
private:
    Node *pre, *head;
public:
    void dfs(Node* cur)
    {
        if (cur == nullptr) return;
        dfs(cur->left);
        if (pre == nullptr) 
            head = cur;
        else
            pre->right = cur;
        cur->left = pre;
        pre = cur;
        dfs(cur->right);
    }

    Node* treeToDoublyList(Node* root) 
    {
        if (root == nullptr)
            return nullptr;
        dfs(root);
        head->left = pre;
        pre->right = head;
        return head;    
    }

};