234. Palindrome Linked List

/**
 * 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 {
    public boolean isPalindrome(ListNode head) {
        if (head == null) {
            return true;
        }
        List<Integer> s = new ArrayList<Integer>();
        int prev = head.val;
        ListNode cur = head.next;
        while (cur != null) {
            s.add(cur.val);
            cur = cur.next;
        }
        int size = s.size() - 1;
        for (int i = 0; i < size / 2; i++) {
            if (s.get(i) != s.get(size - i)) {
                return false;
            }
        }
        
        return true; 
        
    }
}

중간값 고려 x

/**
 * 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 {
    public boolean isPalindrome(ListNode head) {
        if (head == null) {
            return true;
        }
        List<Integer> st = new ArrayList<Integer>();
        ListNode cur = head;
        while (cur != null) {
            st.add(cur.val);
            cur = cur.next;
        }
        int s = 0;
        int e = st.size() - 1;
        
        while (e > s) {
            if (!st.get(s).equals(st.get(e))) {
                return false;
            }
            e--;
            s++;
        }
        
        return true; 
        
    }
}

Runtime: 3 ms, faster than 24.98% of Java online submissions for Palindrome Linked List.

Memory Usage: 43 MB, less than 23.25% of Java online submissions for Palindrome Linked List.

O(1)이 아닌데 귀찮아..