Comet OJ - Contest #7 D 机器学习题 斜率优化 + 未调完

Code:

#include <cstdio>
#include <algorithm>
#include <cstring>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 400005
#define inf 1000000009
#define ll long long
using namespace std;
int head,tail;
int S[maxn];
ll le[maxn],ri[maxn],sumv[maxn],pos[maxn];
ll sqr(ll x)
{
    return 1ll*(1ll*x * 1ll*x);
}
struct Node
{
    ll x,y;
}nd[maxn];
bool cmp(Node a,Node b)
{
    return a.x<b.x;
}
ll Y(int f)
{
    return (ll)(ri[f]+1ll*f*f);
}
ll X(int f)
{
    return f;
}
double slope(int i,int j)
{
    return (double)(Y(i)-Y(j))/(double)(X(i)-X(j));
}
void insert(int x)
{
    if(tail<2)
    {
        if(tail==1)
        {
            if(X(x)==XS[++tail]=x;
        }
        else
        {
            S[++tail]=x;
        }
        return;
    }
    while(tail>1&&slope(S[tail-1], S[tail]) >= slope(S[tail-1], x)) --tail;
    S[++tail]=x;
}
int main()
{
    // setIO("input");
    int n;
    scanf("%d",&n);
    for(int i=1;i<=n;++i) scanf("%lld%lld",&nd[i].x,&nd[i].y);
    sort(nd+1,nd+1+n,cmp);
    nd[0].x=-inf;
    for(int i=1;i<=n;++i) pos[i]=nd[i].x;
    for(int i=1;i<=n;++i)
    {
        sumv[i]=sumv[i-1];
        if(nd[i].y<0) sumv[i]-=nd[i].y;
        le[i]=le[i-1];
        if(nd[i-1].x!=nd[i].x) le[i]=sumv[i-1];
    }
    for(int i=1;i<=n;++i) sumv[i]=0;
    nd[n+1].x=inf;
    for(int i=n;i>=1;--i)
    {
        sumv[i]=sumv[i+1];
        if(nd[i].y>0) sumv[i]+=nd[i].y;
        ri[i]=ri[i+1];
        if(nd[i+1].x!=nd[i].x) ri[i]=sumv[i+1];
    }
    head=1;
    long long ans=100000000000000000;
    for(int i=1;i<=n;++i) insert(i);
    for(int i=1;i<=n;++i)
    {
        while(head<tail && pos[S[head]] < pos[i]) ++head;
        while(head<tail && slope(S[head], S[head+1]) < 2*pos[i]) ++head;
        if(head>tail) break;
        ans=min(ans, le[i] + sqr( (pos[i] - pos[S[head]]) ) + ri[S[head]]);
        // printf("%d %d %lld\n",i,S[head],ans);
    }
    printf("%lld\n",ans);
    return 0;
}