[LeetCode] Sort List 排序 sort

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

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Linked List Sort

 

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　　基于单项链表的排序，时间为nlogn ，O（1）空间，其实及将数组的快速排序用链表实现，并用递归来维护拆分与合并。

#include <iostream>
using namespace std;

/**
 * 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==NULL)  return NULL;
        if(head->next==NULL)    return head;
        ListNode *plft=head,*prgt=head;
        while(prgt->next!=NULL){
            if(prgt->next!=NULL)  prgt=prgt->next;
            if(prgt->next!=NULL)  prgt=prgt->next;
            plft = plft->next;
        }
        if(prgt==head->next){
            if(head->val>prgt->val){
                prgt->next = head;
                head->next = NULL;
                head = prgt;
            }
            return head;
        }
        prgt = plft->next;
        plft->next = NULL;
        plft = sortList(head);
        prgt = sortList(prgt);
        ListNode * ret,*leave,*tmp,*tmp2;
        ret = plft->val<=prgt->val?plft:prgt;
        tmp = ret;
        leave = plft->val<=prgt->val?prgt:plft;
        while(leave!=NULL){
            while(tmp->next!=NULL&&tmp->next->val<=leave->val)  tmp= tmp->next;
            if(tmp->next==NULL){
                tmp->next = leave;
                break;
            }
            tmp2 = leave->next;
            leave->next = tmp->next;
            tmp->next = leave;
            leave = tmp2;
        }
        return ret;
    }
};
//
int main()
{
    ListNode n1(),n2(),n3(),n4(),n5(),n6(),n7();
    n1.next=&n2;
    n2.next=&n3;
    n3.next=&n4;
    n4.next=&n5;
    n6.next=&n7;
    n5.next=&n6;
    Solution sol;
    ListNode * ret = sol.sortList(&n1);
    ListNode * p = ret;
    while(p!=NULL){
        cout<<p->val<<" ";
        p = p->next;
    }
    cout<<endl;
    return ;
}