[leetcode] Merge Two Sorted Lists

Merge Two Sorted Lists

/** Definition for singly-linked list. */

#include <iostream>
using namespace std;

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

class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        if (l1==NULL) {
            return l2;
        }
        if (l2==NULL) {
            return l1;
        }
        //头结点
        ListNode *pHead=NULL;
        
        //默认从小到大排序
        if (l1->val<l2->val) {
            pHead=l1;
            l1=l1->next;
        }else{
            pHead=l2;
            l2=l2->next;
        }
        
        ListNode *pCur=pHead;
        
        while (l1!=NULL&&l2!=NULL) {
            if (l1->val<l2->val) {
                pCur->next=l1;
                l1=l1->next;
            }else{
                pCur->next=l2;
                l2=l2->next;
            }
            pCur=pCur->next;//当前指针后移
        }
        
        if (l1==NULL) {
            pCur->next=l2;
        }else{
            pCur->next=l1;
        }
        
        return pHead;
    }
};

int main(){
    ListNode *p1=new ListNode(5);
    ListNode *p2=new ListNode(1);
    p2->next=new ListNode(2);
    p2->next->next=new ListNode(4);
    
    Solution so;
    ListNode *res= so.mergeTwoLists(p1, p2);
    cout<<res->val<<res->next->val<<res->next->next->val<<res->next->next->next->val<<endl;
    return 0;
}