双指针算法

#include<bits/stdc++.h>
using namespace std;
const int N=5e5+10;
typedef long long ll;
typedef pair<int,int>PII;
vector<PII>v(N),v1(N);
int n,a,b;
int main()
{
    cin>>n>>a>>b;
    for(int i=1;i<=a;i++)
    {
        int x,y;
        cin>>x>>y;
        v[i]={x,y};
    }
    for(int i=1;i<=b;i++)
    {
        int x,y;
        cin>>x>>y;
        v1[i]={x,y};
    }
    ll sum=0;
    int i=1,j=1;
    while(i<=a&&j<=b)
    {
        if(v[i].first!=v1[j].first)
        {
            while(v[i].first!=v1[j].first&&i<=a&&j<=b)
            {
                if(v[i].first<v1[j].first) i++;
                else j++;
            }
        }
        if(i<=a&&j<=b) sum+=(ll)v[i].second*v1[j].second;
        i++,j++;
    }
    cout<<sum<<endl;
    return 0;
}