Palindrome Linked List
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Given a singly linked list, determine if it is a palindrome.
Follow up:
Could you do it in O(n) time and O(1) space?
这种题不希望再错了。明明很简单的。其实leetcode上面的题说白了就是能不能跟你理解的类型联系起来。如果知道类型了,而且也有思路,写不对,很气的。
这道题的思路是:1. 快慢指着找到中间点(都从head开始,找到中间的值。如果是odd, 那么slow停留的位置在正中间;如果希望找到)2. 翻转后半段,这里需要注意在最后返回的时候,再把传入的root节点的next置为空。
代码:
ublic boolean isPalindrome(ListNode head) { if(head == null ||head.next == null ) return true; ListNode slow = head; ListNode fast = head;// 1 2 3 4 5 while(fast.next != null && fast.next.next != null){ slow = slow.next; fast = fast.next.next; } ListNode reverseHead = reverse(slow.next); while(head != null && reverseHead != null){ if(head.val != reverseHead.val){ return false; }else{ head = head.next; reverseHead = reverseHead.next; } } return true; } private ListNode reverse(ListNode node){ ListNode dummy = new ListNode(-1); dummy.next = node; ListNode pre = dummy; ListNode cur = node; while(cur != null){ ListNode next = cur.next; cur.next = pre; pre = cur; cur = next; } node.next = null; return pre; }
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