/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode(int x) : val(x), next(NULL) {}* };*/
class Solution {
public:ListNode* sortList(ListNode* head) {if ( !head || !head->next ) return head;ListNode dummy(-1);dummy.next = head;ListNode *p1=&dummy, *p2=&dummy;while ( p2 && p2->next && p2->next->next ){p1 = p1->next;p2 = p2->next->next;}ListNode *h1 =  Solution::sortList(p1->next);p1->next = NULL;ListNode *h2 =  Solution::sortList(dummy.next);return Solution::mergeTwo(h1, h2);}static ListNode* mergeTwo(ListNode *h1, ListNode *h2){ListNode dummy(-1);ListNode *p = &dummy;while ( h1 && h2 ){if ( h1->val<h2->val ){p->next = h1;h1 = h1->next;}else{p->next = h2;h2 = h2->next;}p = p->next;}p->next = h1 ? h1 : h2;return dummy.next;}
};

/*** Definition for singly-linked list.* struct ListNode {*     int val;*     ListNode *next;*     ListNode(int x) : val(x), next(NULL) {}* };*/
class Solution {
public:ListNode* sortList(ListNode* head){if ( !head ) return NULL;if ( !head->next ) return head;ListNode dummpy(0);ListNode* p1 = &dummpy;ListNode* p2 = &dummpy;dummpy.next = head;while ( p2 && p2->next ){p1 = p1->next;p2 = p2->next->next;}ListNode* r = Solution::sortList(p1->next);p1->next = NULL;ListNode* l = Solution::sortList(dummpy.next);return Solution::merge2SortedLists(l,r);}static ListNode* merge2SortedLists(ListNode* p1, ListNode* p2){ListNode head(0);ListNode* p = &head;while ( p1 && p2 ){if ( p1->val < p2->val ){p->next = p1;p1 = p1->next;}else{p->next = p2;p2 = p2->next;}p = p->next;}p->next = p1 ? p1 : p2;return head.next;}
};