单向链表

#include <iostream>
#include <limits>
#include <vector>
using   namespace   std;

struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) :
            val(x), next(NULL) {
    }
};

class Solution {
public:
    ListNode* Create(vector<int> da) {
        if (da.empty()) return NULL;
        ListNode* head = new ListNode(da[0]);
        ListNode* cur  = head;
        for (int i=1; i<da.size(); ++i) {
            ListNode* a = new ListNode(da[i]);
            cur->next = a;
            cur = cur->next;
        }
        return head;
    }
    void PrintList(ListNode* head) {
        while(head) {
            std::cerr << head->val << " ";
            head = head->next;
        }
        std::cerr << std::endl;
    }
    ListNode* Merge(ListNode* pHead1, ListNode* pHead2)
    {
        if (!pHead1) return pHead2;
        if (!pHead2) return pHead1;
        ListNode* head = pHead1;
        ListNode* per = NULL;
        ListNode* net = NULL;
        while (pHead1 && pHead2) {
            if (pHead1->val <= pHead2->val) {
                per = pHead1;
                pHead1 = pHead1->next;
            } else {
                net = pHead2->next;
                per->next = pHead2;
                pHead2->next = pHead1;
                pHead2 = net;
            }
        }
        if (!pHead1) per->next = pHead2;
        return head;
    }
    ListNode* ReverseList(ListNode* head) {
        if (head == NULL) {
            return NULL;
        }
        ListNode *per = NULL, *cur = head, *net = head->next;
        while (net != NULL) {
            cur->next = per;
            per = cur;
            cur = net;
            net = cur->next;
        }
        cur->next = per;
        return cur;
    }
};

int  main()
{
    vector<int> da{1,3,5};
    vector<int> db{2,4,6};
    Solution s;
    ListNode* head1 = s.Create(da);
    ListNode* head2 = s.Create(db);
    s.PrintList(head1);
    s.PrintList(head2);
    s.PrintList(s.Merge(head1, head2));
    s.PrintList(s.ReverseList(head2));
    return 0;
}