*LeetCode-Palindrome Linked List

翻转first half 然后一个从中间向前 一个向后 进行对比

我自己写的把找到中间和翻转写成了两步 很多错 很麻烦 其实可以写到一起

public class Solution {
    public boolean isPalindrome(ListNode head) {
        if ( head == null || head.next == null )
            return true;
        ListNode fast = head;
        ListNode slow = head;
        ListNode pre = new ListNode (0);
        pre.next = head;
        while ( fast != null && fast.next != null ){
            fast = fast.next.next;
            slow = slow.next;
            pre = pre.next;
        }
        ListNode second = slow;
        if ( fast != null ){
            second = second.next;
        }
        slow = pre;
        ListNode cur = head.next;
        ListNode pre2 = head;
        head.next = null;
        while ( pre2 != slow ){
            ListNode temp = cur.next;
            cur.next = pre2;
            pre2 = cur;
            cur = temp;
        }
        while ( second != null && pre2 != null ){
            if ( second.val != pre2.val )
                return false;
            pre2 = pre2.next;
            second = second.next;
        }
        return true;
    }
}

写到一起的方法

public class Solution {
    public boolean isPalindrome(ListNode head) {
        if ( head == null || head.next == null )
            return true;
        ListNode fast = head;
        ListNode slow = head;
        ListNode pre = new ListNode (0);
        pre.next = head;
        while ( fast != null && fast.next != null ){
            fast = fast.next.next;
            ListNode temp = slow.next;
            slow.next = pre;
            pre = slow;
            slow = temp;
        }
        ListNode second = slow;
        if ( fast != null ){
            second = second.next;
        }
        slow = pre;
        while ( second != null && slow != null ){
            if ( second.val != slow.val )
                return false;
            slow = slow.next;
            second = second.next;
        }
        return true;
    }
}