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234.swift
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234.swift
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/**
* Definition for singly-linked list.
* public class ListNode {
* public var val: Int
* public var next: ListNode?
* public init() { self.val = 0; self.next = nil; }
* public init(_ val: Int) { self.val = val; self.next = nil; }
* public init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next; }
* }
*/
class Solution {
func isPalindrome(_ head: ListNode?) -> Bool {
if head?.next == nil { return true }
var fast = head
var slow = head
var leftlen = 0
while fast?.next != nil {
slow = slow?.next
fast = fast?.next?.next
leftlen += 1
}
// 右边的长度 >= 左边
var right = slow
var n = right?.next
var nn = right?.next?.next
right?.next = nil
while n != nil {
n!.next = right
right = n
n = nn
nn = n?.next
}
var left = head
for _ in 0..<leftlen {
if left!.val != right!.val {
return false
}
left = left!.next
right = right!.next
}
return true
}
}