Leetcode 148. Sort List

文章作者：Tyan
博客：noahsnail.com  |  CSDN  |  简书

1. Description

2. Solution

• Version 1

/**
 * 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) {
            return NULL;
        }
        vector<ListNode*> nodes;
        ListNode* current = head;
        while(current) {
            int index = binarySearch(nodes, current->val);
            nodes.insert(nodes.begin() + index, current);
            current = current->next;
        }
        ListNode* result = nodes[0];
        current = nodes[0];
        for(int i = 1; i < nodes.size(); i++) {
            current->next = nodes[i];
            current = current->next;
        }
        current->next = NULL;
        return result;
    }
    
private:
    int binarySearch(vector<ListNode*>& nodes, int target) {
        int left = 0;
        int right = nodes.size() - 1;
        while(left <= right) {
            int mid = (left + right) / 2;
            if(nodes[mid]->val > target) {
                right = mid - 1;
            }
            else if(nodes[mid]->val < target) {
                left = mid + 1;
            }
            else {
                return mid;
            }
        }
        return left;
    }
};

• Version 2

/**
 * 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* pre = nullptr;
        ListNode* slow = head;
        ListNode* fast = head;
        while (fast != nullptr && fast->next != nullptr) {
            pre = slow;
            slow = slow->next;
            fast = fast->next->next;
        }
        pre->next = nullptr;
        ListNode* l1 = sortList(head);
        ListNode* l2 = sortList(slow);
        return mergeTwoLists(l1, l2);
    }
    
private:
    ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {
        ListNode* ptrFirst = l1;
        ListNode* ptrSecond = l2;
        ListNode* head = new ListNode(0);
        ListNode* current = head;
        while(ptrFirst && ptrSecond) {
            if(ptrFirst->val > ptrSecond->val) {
                current->next = ptrSecond;
                ptrSecond = ptrSecond->next;
            }
            else {
                current->next = ptrFirst;
                ptrFirst = ptrFirst->next;
            }
            current = current->next;
        }
        if(ptrFirst) {
            current->next = ptrFirst;
        }
        if(ptrSecond) {
            current->next = ptrSecond;
        }
        return head->next;
    }
};

Reference

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