AC日记——松江1843路 洛谷七月月赛

松江1843路

思路：

　　三分；

代码：

#include <bits/stdc++.h>
using namespace std;
#define maxn 100005
#define ll long long
struct DataType
{
    ll pi,val,sumval,sumpi;
    bool operator<(const DataType pos)const
    {
        return pi<pos.pi;
    }
};
struct DataType ai[maxn];
ll len,n;
inline void in(ll &now)
{
    char Cget=getchar();now=;
    while(Cget>''||Cget<'')Cget=getchar();
    while(Cget>=''&&Cget<='')
    {
        now=now*+Cget-'';
        Cget=getchar();
    }
}
ll lower(ll key)
{
    ll l=,r=n,res=,mid;
    while(l<=r)
    {
        mid=l+r>>;
        if(key<=ai[mid].pi) res=mid,r=mid-;
        else l=mid+;
    }
    return res;
}
ll calculate(ll key)
{
    ll now=lower(key);
    ll res1=key*ai[now-].sumval-ai[now-].sumpi;
    ll res2=ai[n].sumpi-ai[now-].sumpi-key*(ai[n].sumval-ai[now-].sumval);
    return res2+res1;
}
int main()
{
    in(len),in(n);
    for(ll i=;i<=n;i++) in(ai[i].pi),in(ai[i].val);
    sort(ai+,ai+n+);
    for(ll i=;i<=n+;i++)
    {
        ai[i].sumval=ai[i-].sumval+ai[i].val;
        ai[i].sumpi=ai[i-].sumpi+ai[i].val*ai[i].pi;
    }
    ll l=,r=len,mid,now,nowl,nowr;
    while(l<r)
    {
        mid=l+r>>;
        now=calculate(mid);
        nowl=calculate(mid-);
        nowr=calculate(mid+);
        if(nowl<now) r=mid-;
        else if(nowr<now) l=mid+;
        else
        {
            printf("%lld\n",calculate(mid));
            return ;
        }
    }
    printf("%lld\n",calculate(l));
    return ;
}