2024每日刷题（148）

Leetcode—426. 将二叉搜索树转化为排序的双向链表

实现代码

/*
// 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 {
public:
    Node* treeToDoublyList(Node* root) {
        if(root == nullptr) {
            return (Node*)nullptr;
        }

        // 中序遍历
        stack<Node*> st;
        Node* first = nullptr;
        Node* pre = nullptr;

        while(root != nullptr || !st.empty()) {
            // 左子树全部入栈
            while(root != nullptr) {
                st.push(root);
                root = root->left;
            }

            root = st.top(), st.pop();
            if(first == nullptr) {
                first = root;
            }

            if(pre != nullptr) {
                pre->right = root;
                root->left = pre;
            }

            pre = root;
            root = root->right;
        }

        first->left = pre;
        pre->right = first;
        return first;
    }
};

运行结果

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