题目描述
在O(n log n)的时间内使用常数级空间复杂度对链表进行排序。 Sort a linked list in O(n log n) time using constant space complexity.示例1
输入
{3,2,4}
输出
{2,3,4}
class Solution {public: ListNode* findMiddle(ListNode* head){ ListNode* chaser = head; ListNode* runner = head->next; while(runner != NULL && runner->next != NULL){ chaser = chaser->next; runner = runner->next->next; } return chaser; } ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) { if(l1 == NULL){ return l2; } if(l2 == NULL){ return l1; } ListNode* dummy = new ListNode(0); ListNode* head = dummy; while(l1 != NULL && l2 != NULL){ if(l1->val > l2->val){ head->next = l2; l2 = l2->next; } else{ head->next = l1; l1 = l1->next; } head = head->next; } if(l1 == NULL){ head ->next = l2; } if(l2 == NULL){ head->next = l1; } return dummy->next; } ListNode* sortList(ListNode* head) { if(head == NULL || head ->next == NULL){ return head; } ListNode* middle = findMiddle(head); ListNode* right = sortList(middle->next); middle -> next = NULL; ListNode* left = sortList(head); return mergeTwoLists(left, right); }}; |
