codeforceCodeForces

单调栈

RMQ

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<string>
#include<queue>
#include<map>
#include<set>
#include<list>
#include<ctime>
#include<ctype.h>
#include<bitset>
#include<algorithm>
#include<numeric> //accumulate
#define endl "
"
#define fi first
#define se second
#define FOR(i,s,t) for(int i=(s);i<=(t);++i)
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
const int maxn=300000+5;
long long n,a;
int d[maxn],c[maxn];
long long pref[maxn];
int stc[maxn],top;
int l[maxn],r[maxn];
long long f1[maxn][32];
long long f2[maxn][32];
void rmq_init()
{
    for(int i=1; i<=n; i++)
        f1[i][0]=f2[i][0]=pref[i];
    for(int j=1; (1<<j)<=n; j++)
    {
        for(int i=1; i+(1<<j)-1<=n; i++)
        {
            f1[i][j]=min(f1[i][j-1],f1[i+(1<<(j-1))][j-1]);
            f2[i][j]=max(f2[i][j-1],f2[i+(1<<(j-1))][j-1]);
        }
    }
}
long long rmq_query(int l,int r,int ty)
{
    int k=0;
    while(1<<(k+1)<=r-l+1)
        k++;
    if(ty==0)
        return min(f1[l][k],f1[r-(1<<k)+1][k]);
    else
        return max(f2[l][k],f2[r-(1<<k)+1][k]);

}
int main()
{

    //cin.tie(0);
    //cout.tie(0);
    //ios_base::sync_with_stdio(false);
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    cin>>n>>a;
    for(int i=1; i<=n; i++)
    {
        cin>>d[i]>>c[i];
    }
    for(int i=n; i; i--)
    {
        d[i]=d[i]-d[i-1];
    }
    top=0;
    d[n+1]=1e9;
    for(int i=2; i<=n+1; i++)
    {
        while(top&&d[stc[top]]<d[i])
            r[stc[top--]]=i-1;
        stc[++top]=i;
    }
    d[1]=1e9;
    top=0;
    for(int i=n; i; i--)
    {
        while(top&&d[stc[top]]<d[i])
            l[stc[top--]]=i+1;
        stc[++top]=i;
    }
    //for(int i=2;i<=n;i++)
    //cout<<l[i]<<' '<<r[i]<<endl;
    for(int i=1; i<=n; i++)
    {
        pref[i]=pref[i-1]+a-c[i];
    }
    rmq_init();
    //cout<<rmq_query(1,n,0)<<endl;
    long long ans=0;
    for(int i=2; i<=n; i++)
    {
        long long mi;
        if(i==2) mi=0;
        else if(l[i]==2) mi=min(0ll,rmq_query(1,i-2,0));
        else mi=rmq_query(l[i]-2,i-2,0);
        long long mx=rmq_query(i,r[i],1);
        ans=max(ans,mx-mi-1ll*d[i]*d[i]);
    }
    for(int i=1; i<=n; i++)
    {
        ans=max(ans,1ll*a-c[i]);
    }
    cout<<ans;
}





/*
void read()
{

    char c = getchar();
    int x = 0;
    for (; (c < 48 || c>57); c = getchar());
    for (; c > 47 && c < 58; c = getchar())
    {
        x = (x << 1) + (x << 3) + c - 48;
    }
    return x;
}
*/