1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 | struct ListNode { int val; ListNode *next; ListNode( int x) : val(x), next(NULL) {} }; class Solution { public : void reorderList(ListNode* head) { if (head == nullptr ) return ; int size = 0; ListNode *ptr = head; while (ptr != nullptr ) { size++; ptr = ptr->next; } if (size <= 2) return ; int breakpoint = (size + 1) / 2; int i = 0; ptr = head; while ( i++ < breakpoint) { ptr = ptr->next; } ListNode *ptr2 = head; while (ptr2!= nullptr && ptr2->next != ptr) ptr2 = ptr2->next; if (ptr2 != nullptr ) ptr2->next = nullptr ; ListNode* newheadof2ndPart = reverseLinkedList(ptr); ptr = head; for (i = 0; i< breakpoint && ptr != nullptr && newheadof2ndPart != nullptr ; i++) { ListNode*ptmp = ptr->next; ListNode*pnextnewhead = newheadof2ndPart->next; ptr -> next = newheadof2ndPart; newheadof2ndPart->next = ptmp; ptr = ptmp; newheadof2ndPart = pnextnewhead; } } ListNode* reverseLinkedList(ListNode* head) { if (head == nullptr ) return nullptr ; ListNode* newhead = reverseLinkedList(head->next); if (head-> next != nullptr ) { head->next->next = head; //Error, 一定要搞清楚到底是哪个next哦 } if (newhead == nullptr ) newhead = head; head->next = nullptr ; return newhead; } }; |
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