问题标题: 洛谷：P5094 WA 1分求助

#include<bits/stdc++.h>
using namespace std;
namespace fastIO
{
    #define BUF_SIZE 100000
    bool IOerror=0;
    inline char nc()
    {
        static char buf[BUF_SIZE],*p1=buf+BUF_SIZE,*pend=buf+BUF_SIZE;
        if(p1==pend)
        {
            p1=buf;
            pend=buf+fread(buf,1,BUF_SIZE,stdin);
            if(pend==p1)
            {
                IOerror=1;
                return -1;
            }
        }
        return *p1++;
    }
    inline bool blank(char ch)
    {
        return ch==' '||ch=='\n'||ch=='\r'||ch=='\t';
    }
    inline void read(int &x)
    {
        char c;
        while(blank(c=nc()));
        if(IOerror) return;
        for(x=c-'0';(c=nc())>='0'&&c<='9';x=x*10+c-'0');
    }
    #undef BUF_SIZE
};
long long n,ans; 
typedef long long ll;
struct io
{
    int x,y;
} a[50000];
inline bool cmp(io a,io b)
{
    return a.x<b.x;
}
inline void write(long long x){
    if(x<0){
        putchar('-');
        x=-x;
    }
    if(x>9)write(x/10);
    putchar(x%10+'0');
}
int main()
{
    cin>>n;
    for(register int i=1;i<=n;i++)
        fastIO::read(a[i].x),fastIO::read(a[i].y);
    sort(a+1,a+n+1,cmp);
    for(register int i=2;i<=n;i++)
        for(register int j=1;j<i;j++)
            ans+=a[i].x*abs(a[i].y-a[j].y);
    write(ans);
    return 0;
}

思路：模拟，卡常

有啥优化算法吗，为什么1分