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  • #Leetcode# 148. Sort List

    https://leetcode.com/problems/sort-list/ 

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

    Example 1:

    Input: 4->2->1->3
    Output: 1->2->3->4
    

    Example 2:

    Input: -1->5->3->4->0
    Output: -1->0->3->4->5

    代码:

    /**
     * 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 *fast = head, *slow = head, *pre = head;
            while(fast && fast -> next) {
                pre = slow;
                slow = slow -> next;
                fast = fast -> next -> next;
            }
            pre -> next = NULL;
            return mergesort(sortList(head), sortList(slow));
        }
        ListNode *mergesort(ListNode* l1, ListNode* l2) {
            ListNode *dummy = new ListNode(-1);
            ListNode *cur = dummy;
            while(l1 && l2) {
                if(l1 -> val < l2 -> val) {
                    cur -> next = l1;
                    l1 = l1 -> next;
                } else {
                    cur -> next = l2;
                    l2 = l2 -> next;
                }
                
                cur = cur -> next;
            }
            
            if(l1) cur -> next = l1;
            if(l2) cur -> next = l2;
            return dummy -> next;
        }
    };
    

      归并排序 学到了

    FHFHFH

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  • 原文地址:https://www.cnblogs.com/zlrrrr/p/10337874.html
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