没啥好说的，写一下指针练一练，用指针挺容易出错的细节挺多

#include<bits/stdc++.h>
#define ULL unsigned long long 
#define DB double
#define LL long long
using namespace std;
int n,m,i,j;
struct QNode
{
	int shu,ci;
	QNode* nt;
}*headA,*headB,*tailA,*tailB,*headAns,*tailAns;
void InitQ(QNode *&b,QNode *&e)
{
	b=e=new QNode;
	b->nt=e->nt=NULL;
}
void ru(QNode *&l,int shu,int ci)
{
	QNode *p=new QNode;
	p->shu=shu;p->ci=ci;p->nt=NULL;
	l->nt=p;l=p;
}
int main()
{
	cin>>n>>m;
	InitQ(headA,tailA);InitQ(headB,tailB);InitQ(headAns,tailAns);
	for(int i=1,shu,ci;i<=n;++i)scanf("%d%d",&shu,&ci),ru(tailA,shu,ci);
	for(int i=1,shu,ci;i<=m;++i)scanf("%d%d",&shu,&ci),ru(tailB,shu,ci);
	i=j=1;
	headA=headA->nt;headB=headB->nt;
	while(headA!=NULL&&headB!=NULL)
	{
		if(headA->ci==headB->ci)ru(tailAns,headA->shu+headB->shu,headA->ci),headA=headA->nt,headB=headB->nt;
		else if(headA->ci<headB->ci)ru(tailAns,headA->shu,headA->ci),headA=headA->nt;
		else ru(tailAns,headB->shu,headB->ci),headB=headB->nt;
	}
	while(headA!=NULL)ru(tailAns,headA->shu,headA->ci),headA=headA->nt;
	while(headB!=NULL)ru(tailAns,headB->shu,headB->ci),headB=headB->nt;
	headAns=headAns->nt;
	while(headAns!=NULL)
	{
		if(headAns->shu)printf("%d %d\n",headAns->shu,headAns->ci);
		headAns=headAns->nt;
	}
	return 0;
}