【Violet 6】【BZOJ2724】蒲公英

Description



Input



修正一下

l = (l_0 + x - 1) mod n + 1, r = (r_0 + x - 1) mod n + 1

Output



Sample Input

6 3

1 2 3 2 1 2

1 5

3 6

1 5

Sample Output

1

2

1

HINT



修正下：

n <= 40000, m <= 50000

Source

Vani原创

区间众数.

想了一段时间线段树感觉不科学T_T

观察数据范围也不像线段树啊…

然后去感受了一下发现是分块…

跟着黄学长领悟了人生第一个分块…(求不D

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#define MAXN 40010
#define GET (ch>='0'&&ch<='9')
using namespace std;
int n,m,size,cnt,maxn,Ans,lastans;
int a[MAXN],belong[MAXN],first[300],last[300],Count[MAXN];
int hash[MAXN],L[MAXN],R[MAXN];
int ans[300][300];//块间答案
struct Num
{
int pos,x;
bool operator <(const Num& a)const  {return x==a.x?pos<a.pos:x<a.x;}
}s[MAXN];
void in(int &x)
{
char ch=getchar();x=0;
while (!GET)    ch=getchar();
while (GET) x=x*10+ch-'0',ch=getchar();
}
int find(int x)
{
int l=1,r=n,mid;
while (l<=r)
{
mid=(l+r)>>1;
if (hash[mid]<x)    l=mid+1;
else    if (hash[mid]>x)    r=mid-1;
else    return mid;
}
}
int upper(int l,int r,int x)//不会用STL星人
{
int ret=0,mid;
while (l<=r)
{
mid=(l+r)>>1;
if (s[mid].pos>x)   r=mid-1;
else    ret=mid,l=mid+1;
}
return ret;
}
int lower(int l,int r,int x)
{
int ret=0,mid;
while (l<=r)
{
mid=(l+r)>>1;
if (s[mid].pos<x)   l=mid+1;
else    ret=mid,r=mid-1;
}
return ret;
}
int query(int l,int r)
{
int ret;maxn=0;
if (belong[l]==belong[r])
{
for (int i=l;i<=r;i++)
{
int Cnt=upper(L[a[i]],R[a[i]],r)-lower(L[a[i]],R[a[i]],l)+1;
if (Cnt>maxn||(Cnt==maxn&&a[i]<ret))    maxn=Cnt,ret=a[i];
}
return ret;
}
if (belong[l]+1<belong[r])  ret=ans[belong[l]+1][belong[r]-1],maxn=upper(L[ret],R[ret],r)-lower(L[ret],R[ret],l)+1;
for (int i=l;i<=last[belong[l]];i++)
{
int Cnt=upper(L[a[i]],R[a[i]],r)-lower(L[a[i]],R[a[i]],l)+1;
if (Cnt>maxn||(Cnt==maxn&&a[i]<ret))    maxn=Cnt,ret=a[i];
}
for (int i=first[belong[r]];i<=r;i++)
{
int Cnt=upper(L[a[i]],R[a[i]],r)-lower(L[a[i]],R[a[i]],l)+1;
if (Cnt>maxn||(Cnt==maxn&&a[i]<ret))    maxn=Cnt,ret=a[i];
}
return ret;
}
int main()
{
in(n);in(m);size=(int)(sqrt(n));cnt=n/size+(bool)(n%size);//划分块
for (int i=1;i<=n;i++)  in(a[i]),hash[i]=a[i],belong[i]=(i-1)/size+1;
for (int i=1;i<=cnt;i++)    first[i]=size*(i-1)+1,last[i]=size*i;
sort(hash+1,hash+n+1);
for (int i=1;i<=n;i++)  a[i]=find(a[i]);//离散
for (int i=1;i<=n;i++)  s[i].x=a[i],s[i].pos=i;
sort(s+1,s+n+1);int l,r;
for (int i=1;i<=n;i++)//记录每个数出现左右区间
{
if (!L[s[i].x]) L[s[i].x]=i;
R[s[i].x]=i;
}
for (int i=1,t;i<=cnt;i++)
{
memset(Count,0,sizeof(Count));maxn=0;
for (int j=first[i];j<=n;j++)
{
Count[a[j]]++;
if (Count[a[j]]>maxn||(Count[a[j]]==maxn&&a[j]<t))  maxn=Count[a[j]],t=a[j];
ans[i][belong[j]]=t;
}
}
for (int i=1;i<=m;i++)
{
in(l);in(r);l=(l+lastans-1)%n+1;r=(r+lastans-1)%n+1;
if (l>r)    swap(l,r);
Ans=hash[query(l,r)];lastans=Ans;
printf("%d\n",Ans);
}
}