list

一，Sort List

题目描述

Sort a linked list in O(n log n) time using constant space complexity.

 

我的代码

/** * Definition for singly-linked list. * struct ListNode { *     int val; *     ListNode *next; *     ListNode(int x) : val(x), next(NULL) {} * }; */class Solution {public:    ListNode* getMiddleNodeOfList(ListNode* head){        ListNode* slow = head;        ListNode* fast = head;        if(head == NULL){            return NULL;        }        while(fast->next != NULL && fast->next->next != NULL) {            slow = slow->next;            fast = fast->next->next;        }        return slow;    }    ListNode* sortList(ListNode* head) {        if(head == NULL || head->next == NULL) {            return head;        }        ListNode *middle = getMiddleNodeOfList(head);        ListNode *next   = middle->next;        middle->next = NULL;        return mergeList(sortList(head), sortList(next));    }    ListNode* mergeList(ListNode *list1, ListNode *list2){        ListNode *head = new ListNode(-1);        ListNode *p1, *p2, *pre = head;        p1 = list1;        p2 = list2;        head->next = NULL;        while(p1 != NULL && p2 != NULL){            if(p1->val < p2->val){                pre->next = p1;                pre = p1;                p1 = p1->next;            } else {                pre->next = p2;                pre = p2;                p2 = p2->next;            }        }        if(p1 != NULL){            pre->next = p1;        }        if(p2 != NULL){            pre->next = p2;        }        return head->next;    }};