package main

import "fmt"

// ListNode Definition for singly-linked list.
type ListNode struct {
	Val  int
	Next *ListNode
}

func isPalindrome(head *ListNode) bool {
	srcHead := head
	head = head.Next
	// var left, right *ListNode
	cnt := 1
	for head != nil {
		head = head.Next
		cnt++
	}
	head = srcHead.Next
	lastNode := srcHead
	srcHead.Next = nil
	half := cnt / 2
	half--
	for range half {
		p := head.Next
		head.Next = lastNode
		lastNode = head
		head = p
	}
	if cnt&1 == 1 {
		head = head.Next
	}
	for head != nil && lastNode != nil {
		if head.Val != lastNode.Val {
			return false
		}
		head = head.Next
		lastNode = lastNode.Next
	}
	if head != nil || lastNode != nil {
		return false
	}
	return true
}

func main() {
	isPalindrome := isPalindrome(&ListNode{
		Val: 1,
		Next: &ListNode{
			Val: 2,
		},
	})
	fmt.Printf("isPalindrome: %v\n", isPalindrome)
}