剑指OFFER----36、二叉搜索树与双向链表(js实现)

题目

• 输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。
• leetcode链接：https://leetcode-cn.com/problems/er-cha-sou-suo-shu-yu-shuang-xiang-lian-biao-lcof/

---

思路

• 先中序遍历进行right指向
• 再从头开始遍历，依据right指向进行left指向
• 头尾互连

---

代码

/**
 * // Definition for a Node.
 * function Node(val,left,right) {
 *    this.val = val;
 *    this.left = left;
 *    this.right = right;
 * };
 */
/**
 * @param {Node} root
 * @return {Node}
 */
var treeToDoublyList = function(root) {
    if (!root) return null
    if (!root.left && !root.right) {
        root.left = root
        root.right = root
        return root
    }
    let firstNode = null
    let lastNode = null
    let prevNode = null
    function order(node) {
        if (!node) return
        order(node.left)
        if (!firstNode) firstNode = node
        if (!prevNode) {
            prevNode = node
        } else {
            prevNode.right = node
            prevNode = node
        }
        order(node.right)
    }
    order(root)
    let node = firstNode
    while (node.right) {
        node.right.left = node
        node = node.right
        lastNode = node
    }
    firstNode.left = lastNode
    lastNode.right = firstNode
    return firstNode
};