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public class PalindromeLinkedList {

// 耗时2ms

public boolean isPalindrome(ListNode head) {

ListNode slow = head, fast = head;

while (fast != null && fast.next != null) {

slow = slow.next;

fast = fast.next.next;

}

fast = reverse(slow);

/**

* 注意退出条件是p1 != slow

*/

for (ListNode p1 = head, p2 = fast; p1 != slow; p1 = p1.next, p2 = p2.next) {

if (p1.val != p2.val) {

return false;

}

}

return true;

}

private ListNode reverse(ListNode node) {

ListNode dummy = new ListNode(0), cur = dummy;

while (node != null) {

ListNode next = node.next;

node.next = cur.next;

cur.next = node;

node = next;

}

return dummy.next;

}

}