bzoj4700

题解：

cdq分治

先考虑没有人被秒掉的情况

代码：

#include<bits/stdc++.h>
#define y1 ____y1
const int N=;
using namespace std;
typedef long long ll;
int bh[N],q[N],bhd[N],bha[N],A[N],d[N],P[N],T[N],n,atk;
ll ans,pr,K[N];
int comp1(const int x,const int y)
{
    return A[x]*d[y]>A[y]*d[x];
}
int fc(int x,int y,int z)
{
    ll x1=d[x],y1=K[x],x2=d[y],y2=K[y],x3=d[z],y3=K[z];
    return (y1-y2)*(x2-x3)>=(y2-y3)*(x1-x2);
}
void cdq(int xl,int xr)
{
    if (xl==xr)return;
    int mid=xl+xr>>;
    cdq(xl,mid);cdq(mid+,xr);
    int l=,r=;
    for (int i=xl;i<=mid;i++)
     {
        while (l<r&&fc(bhd[i],q[r],q[r-]))r--;
        q[++r]=bhd[i];
     }
    for (int i=mid+;i<=xr;i++)
     {
        while (l<r&&K[q[l]]-K[q[l+]]<=(ll)A[bha[i]]*(d[q[l]]-d[q[l+]]))l++;
        if (l<=r)ans=max(ans,K[bha[i]]+K[q[l]]-(ll)A[bha[i]]*d[q[l]]);
     }
    int i=xl,j=mid+,ptr=xl;
    for (;i<=mid&&j<=xr;)
     {
        if (d[bhd[i]]<d[bhd[j]])bh[ptr++]=bhd[i++];
        else bh[ptr++]=bhd[j++];
     }
    for (;i<=mid;)bh[ptr++]=bhd[i++];
    for (;j<=xr;)bh[ptr++]=bhd[j++];
    for (int i=xl;i<=xr;i++)bhd[i]=bh[i];
    i=xl,j=mid+,ptr=xl;
    for (;i<=mid&&j<=xr;)
     {
        if (d[bha[i]]<d[bha[j]])bh[ptr++]=bha[i++];
        else bh[ptr++]=bha[j++];
     }
    for (;i<=mid;)bh[ptr++]=bha[i++];
    for (;j<=xr;)bh[ptr++]=bha[j++];
    for (int i=xl;i<=xr;i++)bha[i]=bh[i];
}
int main()
{
    scanf("%d%d",&n,&atk);
    for (int i=;i<=n;i++)bh[i]=i;
    for (int i=;i<=n;i++)
     {
        scanf("%d%d",&A[i],&d[i]);
        d[i]=(d[i]-)/atk+;
     }
    sort(bh+,bh+n+,comp1);
    for (int i=;i<=n;i++)
     {
        P[i]=P[i-]+d[bh[i]];
        T[i]=T[i-]+A[bh[i]];
        bhd[i]=bha[i]=bh[i];
     }
    for (int i=;i<=n;i++)
     {
        K[bh[i]]=(ll)A[bh[i]]*(P[i]-)+(ll)(T[n]-T[i])*d[bh[i]];
        pr+=(ll)A[bh[i]]*(P[i]-);
     }
    cdq(,n);
    printf("%lld",pr-ans);
    return ;
}