109. Convert Sorted List to Binary Search Tree（js）

109. Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

Example:

Given the sorted linked list: [-10,-3,0,5,9],

One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:

      0
     / 
   -3   9
   /   /
 -10  5
题意：将排好序的链表转化成深度相等的二叉树
代码如下：

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * Definition for a binary tree node.
 * function TreeNode(val) {
 *     this.val = val;
 *     this.left = this.right = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {TreeNode}
 */
var sortedListToBST = function(head) {
    if(!head) return null;
    if(!head.next) return new TreeNode(head.val);
    let slow=head,fast=head,last=slow;
    while(fast.next && fast.next.next){
        last=slow;
        slow=slow.next;
        fast=fast.next.next;
    }
    fast=slow.next;
    last.next=null;
    
    let cur=new TreeNode(slow.val);
    if(head!==slow) cur.left=sortedListToBST(head);
    cur.right=sortedListToBST(fast);
    return cur;
};