Sort a linked list in O(n log n) time using constant space complexity.
C++
/** * 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* slow = head; ListNode* fast = head; ListNode* pre = head; while (fast && fast->next){ pre = slow; slow = slow->next; fast = fast->next->next; } pre->next = NULL; return merge(sortList(head),sortList(slow)); } ListNode* merge(ListNode* left,ListNode* right){ ListNode *head; if (left->val < right->val){ head = left; left = left->next; }else{ head = right; right = right->next; } ListNode *cur = head; while(left && right){ if (left->val < right->val){ cur->next = left; left = left->next; }else{ cur->next = right; right = right->next; } cur = cur->next; } if (left) cur->next = left; if (right) cur->next = right; return head; } ListNode* merge2(ListNode*left, ListNode* right){ ListNode* head = new ListNode(-1); ListNode* cur = head; while(left && right){ if (left->val < right->val){ cur->next = left; left = left->next; }else{ cur->next = right; right = right->next; } cur = cur->next; } if (left) cur->next = left; if (right) cur->next = right; return head->next; } };
转载于:https://www.cnblogs.com/vercont/p/10210249.html
