LeetCode - Sort List C++

real_lisa

已于 2022-10-02 06:18:47 修改

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分类专栏： LeetCode 文章标签： leetcode 算法 array C++

于 2018-09-18 16:51:35 首次发布

本文链接：https://blog.youkuaiyun.com/real_lisa/article/details/82756668

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本文详细介绍了使用快速排序和归并排序两种算法对链表进行排序的方法，包括算法实现和复杂度分析。

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解法一：

快速排序

class Solution {
public:
    ListNode* sortList(ListNode* head) {
        if(!head || !head->next) return head;
        ListNode* cur = head->next;
        ListNode* small = new ListNode(0);
        ListNode* large = new ListNode(0);
        ListNode* sp = small;
        ListNode* lp = large;
        while(cur){
            if(cur->val<head->val){
                sp->next = cur;
                sp = cur;
            } 
            else{
                lp->next = cur;
                lp = cur;
            }
            cur = cur->next;
        }
        sp->next = NULL;
        lp->next = NULL;
        small=sortList(small->next);
        large=sortList(large->next);
        cur = small;
        if(cur){
            while(cur->next) cur = cur->next;
            cur->next = head;
            head->next = large;
            return small;
        }else{
            head->next = large;
            return head;
        }
    }
};

解法二：

归并排序

class Solution {
public:
    ListNode* merge(ListNode* p1, ListNode* p2){
        ListNode* res = new ListNode(0);
        ListNode* cur = res;
        while(p1 && p2){
            if(p1->val<p2->val){
                cur->next = p1;
                p1 =p1->next;
            }else{
                cur->next = p2;
                p2 = p2->next;
            }
            cur = cur->next;
        }
        
        if (p1) cur->next = p1;
        if (p2) cur->next = p2;
        
        return res->next;
    }
    ListNode* sortList(ListNode* head) {
        if(!head || !head->next) return head;
        ListNode* fast = head;
        ListNode* slow = head;
        ListNode* pre = head;
        while(fast && fast->next){
            pre = slow;
            fast = fast->next->next;
            slow = slow->next;
        }
        pre->next = NULL;
        return merge(sortList(head), sortList(slow));
    }
};