g0201_0300.s0234_palindrome_linked_list.Solution.swift Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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// #Easy #Top_100_Liked_Questions #Two_Pointers #Stack #Linked_List #Recursion
// #Level_2_Day_3_Linked_List #Udemy_Linked_List #Big_O_Time_O(n)_Space_O(1)
// #2024_07_01_Time_290_ms_(100.00%)_Space_22.1_MB_(36.73%)

/**
 * 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 {
        var arr = [Int]()
        var head = head
        while let node = head  {
            arr.append(node.val)
            head = node.next
        }
        var i = 0
        var j = arr.count-1
        while i < j {
            if arr[i] != arr[j] {
                return false
            }
            i += 1
            j -= 1
        }
        return true
    }
}