[LeetCode]97. Reorder List链表重排序

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        if(head == NULL || head->next == NULL) return;
        ListNode *slow = head, *fast = head;
        while(fast->next != NULL && fast->next->next != NULL) {
            slow = slow->next;
            fast = fast->next->next;
        }        
        ListNode* head1 = head;
        ListNode* head2 = slow->next;
        head2 = reverseList(head2);
        slow->next = NULL;
        while(head2 != NULL) {
            ListNode *next1 = head1->next, *next2 = head2->next;
            head1->next = head2;
            head2->next = next1;
            head1 = next1;
            head2 = next2;
        }
    }
private:
    ListNode* reverseList(ListNode* head) {
        ListNode* rHead = NULL;
        ListNode* curr = head;
        ListNode* pTail = NULL;
        while(curr != NULL) {
            ListNode* pNext = curr->next;
            if(pNext == NULL)
                rHead = curr;
            curr->next = pTail;
            pTail = curr;
            curr = pNext;
        }
        return rHead;
    }
};