题解 | #判断一个链表是否为回文结构#

/*
 * function ListNode(x){
 *   this.val = x;
 *   this.next = null;
 * }
 */

/**
 * 
 * 把单向链表改为双向链表，从头和尾同步遍历，遇到不等return false, 否则最后return true
 */
function isPail( head ) {
    // write code here
    let current = head;
    let tail;
    while(current){

        if(current.next == null){

            tail=current;
        }
        else{
            current.next.prev = current;
        }
        current = current.next;
    }

    while(head && tail){
        if(head.val != tail.val){
            return false;
        }
        if(head.next===tail||head.next===tail.prev){
            break;
        }
        head = head.next;
        tail = tail.prev;
    }
    return true;
}
module.exports = {
    isPail : isPail
};