和區間眾數幾乎一模一樣的套路。

// luogu-judger-enable-o2
#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 100010
#define BLOCK 350
int n,m,c,a[N],lastans=0;
int block,tot,L[N],R[N],pos[N];
int cnt[N],f[BLOCK][BLOCK],sum[BLOCK][N];
int main()
{
    freopen("bzoj2821.in","r",stdin);
    freopen(
 
"bzoj2821.out","w",stdout);
    n=read(),c=read(),m=read();
    for (int i=1;i<=n;i++) a[i]=read();
    block=sqrt(n);tot=n/block+(n%block>0);
    for (int i=1;i<=n/block;i++)
    L[i]=(i-1)*block+1,R[i]=(i-1)*block+block;
    if (n/block<tot) L[tot]=n/block*block+1,R[tot]=n;
    for (int i=1
 
;i<=tot;i++)
    {
        memset(cnt,0,sizeof(cnt));
        for (int j=i;j<=tot;j++)
        {
            f[i][j]=f[i][j-1];
            for (int k=L[j];k<=R[j];k++)
            {
                cnt[a[k]]++;
                if (!(cnt[a[k]]&1)) f[i][j]++;
                else if (cnt[a[k]]>1) f[i][j]--;
            }
        }
        memcpy(sum[i],sum[i-1],sizeof(sum[i]));
        for (int j=L[i];j<=R[i];j++)
        pos[j]=i,sum[i][a[j]]++;
    }
    memset(cnt,0,sizeof(cnt));
    while (m--)
    {
        int x=read(),y=read();
        x=(x+lastans)%n+1,y=(y+lastans)%n+1;
        if (x>y) swap(x,y);
        int num=0;
        if (pos[x]==pos[y])
        {
            for (int i=x;i<=y;i++)
            {
                cnt[a[i]]++;
                if (!(cnt[a[i]]&1)) num++;
                else if (cnt[a[i]]>1) num--;
            }
            for (int i=x;i<=y;i++) cnt[a[i]]--;
        }
        else
        {
            num=f[pos[x]+1][pos[y]-1];
            for (int i=x;i<=R[pos[x]];i++)
            {
                cnt[a[i]]++;
                if (!(cnt[a[i]]+sum[pos[y]-1][a[i]]-sum[pos[x]][a[i]]&1)) num++;
                else if (cnt[a[i]]+sum[pos[y]-1][a[i]]-sum[pos[x]][a[i]]>1) num--;
            }
            for (int i=L[pos[y]];i<=y;i++)
            {
                cnt[a[i]]++;
                if (!(cnt[a[i]]+sum[pos[y]-1][a[i]]-sum[pos[x]][a[i]]&1)) num++;
                else if (cnt[a[i]]+sum[pos[y]-1][a[i]]-sum[pos[x]][a[i]]>1) num--;
            }
            for (int i=x;i<=R[pos[x]];i++) cnt[a[i]]--;
            for (int i=L[pos[y]];i<=y;i++) cnt[a[i]]--;
        }
        lastans=num;
        printf("%d\n",num);
    }
    return 0;
}

BZOJ2821 作詩（分塊）