BZOJ3613 HEOI2014南园满地堆轻絮

　　不明白在某谷上是怎么标到紫的。二分答案或者发现答案就是最大逆序差的一半。

#include<iostream> 
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
using namespace std;
int read()
{
    int x=0,f=1;char c=getchar();
    while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
    while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
    return x*f;
}
#define N 5000010
int n,a[N],P,w,x,y,z;
int f(int t){return ((1ll*w*t%P*t%P*t%P+1ll*x*t%P*t%P)%P+(1ll*y*t%P+z)%P)%P;}
bool check(int x)
{
    int last=0;
    for (int i=1;i<=n;i++)
    if (a[i]>=last) last=max(last,a[i]-x);
    else if (last-a[i]>x) return 0;
    return 1;
}
int main()
{
#ifndef ONLINE_JUDGE
    freopen("bzoj3613.in","r",stdin);
    freopen("bzoj3613.out","w",stdout);
    const char LL[]="%I64d\n";
#else
    const char LL[]="%lld\n";
#endif
    n=read(),w=read(),x=read(),y=read(),z=read(),a[1]=read(),P=read();
    for (int i=2;i<=n;i++)
    a[i]=(f(a[i-1])+f(a[i-2]))%P;
    int l=0,r=P,ans=0;
    while (l<=r)
    {
        int mid=l+r>>1;
        if (check(mid)) ans=mid,r=mid-1;
        else l=mid+1;
    }
    cout<<ans;
    return 0;
}