package main

import "fmt"

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

func makeLink(arr []int) *ListNode {
	if len(arr) == 0 {
		return nil
	}
	head := &ListNode{}
	cur := head
	for _, v := range arr {
		cur.Next = &ListNode{Val: v}
		cur = cur.Next
	}
	return head.Next
}
func checkLink(head *ListNode) {
	for head != nil {
		fmt.Println(head.Val)
		head = head.Next
	}
}

func reverseBetween(head *ListNode, left int, right int) *ListNode {
	if head.Next == nil {
		return head
	}
	left--
	right--
	cur_idx := 0
	cur := head
	var left_node *ListNode
	var left_pre_node *ListNode = nil
	_ = left_pre_node
	var last_node *ListNode = nil
	do_rev := false

	for {
		if cur_idx == left {
			left_node = cur
			left_pre_node = last_node
			do_rev = true
		}
		next := cur.Next
		if do_rev {
			next = cur.Next
			cur.Next = last_node
			if cur_idx == right {
				left_node.Next = next
				if left_pre_node != nil {
					left_pre_node.Next = cur
				} else {
					head = cur
				}
				do_rev = false
			}
		}
		last_node = cur
		cur = next
		cur_idx++
		if cur == nil {
			break
		}
	}
	return head
}

func main() {
	arr := []int{3, 5}
	checkLink(reverseBetween(makeLink(arr), 1, 2))
}