Sword refers to offer 36. Binary search tree and doubly linked list

Sword refers to offer 36. Binary search tree and doubly linked list

Title description

Problem-solving ideas

The in-order traversal of the binary search tree is the sequential linked list.

This question also uses the method of in-order traversal of the record predecessor .

class Solution {
    
    
    Node head, pre;
    public Node treeToDoublyList(Node root) {
    
    
        if (root == null) return null;
        //将树转化为双向链表，pre最后停留在尾节点上
        inorderTraversal(root);
        //将 双向链表 转化为 双向循环链表
        head.left = pre;
        pre.right = head;
        return head;
    }
    
    //中序遍历，将以root为根节点的树转化为双向链表
    public void inorderTraversal(Node root) {
    
    
        if (root == null) return;
        inorderTraversal(root.left);

        if (pre != null) {
    
    
            pre.right = root;
        } else {
    
    
            head = root;   //双向链表的头结点
        }
        root.left = pre;
        pre = root;   //记录前驱

        inorderTraversal(root.right);
    }
}