leetcode - 234. Palindrome Linked List【判断回文链表 + 双指针 + O(1)空间复杂度】
2017-08-21 23:47
459 查看
题目
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?
分析及解答
解法1:(利用栈)class Solution {
public boolean isPalindrome(ListNode head) {
LinkedList<ListNode> stack = new LinkedList<>();
ListNode p = head;
while(p != null){
stack.push(p);
p = p.next;
}
p = head;
while(p != null && !stack.isEmpty()){
if(p.val != stack.pop().val){
return false;
}
p = p.next;
}
return true;
}
解法2:(改变链表 + 双指针)
class Solution {
public boolean isPalindrome(ListNode head) {
if(head == null){
return true;
}
ListNode p = head;
int nodeNum = 0;
while(p != null){ //统计结点的数量
nodeNum ++;
p = p.next;
}
p = head;
ListNode p2 = head.next;
head.next = null;
for(int i = 1; i < nodeNum/2;i++){ //将前半部分反转,一次改变一个指针。假如说有M个结点,那么有M-1个指针,循环M-1次。
ListNode tmp = p2.next;
p2.next = p;
p = p2;
p2 = tmp;
}
if(nodeNum%2 != 0 && p2 != null){ //考虑奇数的情况,跳过最中间的元素。
p2 = p2.next;
}
while(p != null && p2 != null){ //若只有一个结点,直接跳过
if(p.val != p2.val){
return false;
}
p = p.next;
p2 = p2.next;
}
return true;
}
}
相关文章推荐
- leetcode 234. Palindrome Linked List 回文链表的判断 + 双指针
- LeetCode 234. Palindrome Linked List判断链表是否回文
- 【Leetcode】234. Palindrome Linked List -判断链表是否为回文序列
- leetcode 234. Palindrome Linked List-回文链表|双指针
- Leetcode-234. Palindrome Linked List(判断链表是否回文)
- [LeetCode] 234. Palindrome Linked List 回文链表
- LeetCode234_PalindromeLinkedList (判断是否为回文链表) Java题解
- LeetCode 234. Palindrome Linked List (回文链表)
- [分析总结:leetcode-Palindrome Linked List] 给定单链表,判断链表是否为回文。
- LeetCode:234. Palindrome Linked List 回文链表 Java
- 234. Palindrome Linked List 判断链表是否回文(C++解决)
- Palindrome Linked List - LeetCode 判断一个链表是否是回文结构
- LeetCode:Palindrome Linked List(回文链表)
- leetcode--Linked List Cycle--判断链表是否有环
- leetcode 328 --Odd Even Linked List 链表 双指针 移动节点
- C实现 LeetCode->Linked List Cycle 双指针大法)(单链表是否有环)
- (LeetCode)Palindrome Linked List --- 单链表回文
- [leetcode 141] Linked List Cycle----判断链表是否为循环链表
- C实现 LeetCode->Reverse Linked List II (双指针大法)(单链表反转)
- LeetCode | Linked List Cycle(判断链表是否有环)