《leetCode》：Palindrome Linked List

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?

思路

此题比较简单，具体思路如下：
将一个链表分成两半，然后将后面这个链表进行翻转，最后就对这两个链表从后到尾进行比较即可。

struct ListNode * reverseList(struct ListNode *head){
    if(head==NULL){
        return NULL;
    }
    struct ListNode * cur=head;
    struct ListNode * pre=NULL;
    struct ListNode * next=NULL;
    while(cur!=NULL){
        next=cur->next;
        cur->next=pre;
        pre=cur;
        cur=next;
    }
    return pre;
}
bool isPalindrome(struct ListNode* head) {
      if(head==NULL){

          return true;
      } 
      struct ListNode * cur=head;
      struct ListNode* pre=NULL;
      int len=0;
      while(cur!=NULL){
          len++;
          cur=cur->next;
      }
      if(len==1){
          return true;
      }
      cur=head;
      int k=len/2;

      while(k>0){
          pre=cur;
          cur=cur->next;
          k--;
      }
      struct ListNode *newhead=cur;
      pre->next=NULL;
      cur=head;
      struct ListNode * otherHead=reverseList(newhead);
      struct ListNode * cur1=otherHead;
      int tempLen=len/2;
      while(cur!=NULL){
          int temp1=cur->val;
          int temp2=cur1->val;
          if(temp1!=temp2){
              return false;
          }
          cur=cur->next;
          cur1=cur1->next;

      }
      return true;
}