234. Palindrome Linked List

정리 코드

Recursion Function(재귀함수) : 자기 자신을 재참조, 종료 조건으로 종료 시점을 제어한다.

leetcode : 234. Palindrome Linked List

• 조건
  • The number of nodes in the list is in the range [1, 105].
  • 0 <= Node.val <= 9

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
  private ListNode current;

  public boolean isPalindrome(ListNode head) {
    current = head;
    return isPalindromeHelper(head);
  }

  public boolean isPalindromeHelper(ListNode node) {
    if (node == null) {
      return true;
    }
    boolean isPalindromeTail = isPalindromeHelper(node.next);
    boolean isPalindromeCurrent = (current.val == node.val);
    current = current.next;
    return isPalindromeTail && isPalindromeCurrent;
  }
}