UVA-11536 Smallest Sub-Array

# include<iostream>
# include<cstdio>
# include<cstring>
# include<algorithm>
using namespace std;

const int INF=1<<30;
int n,m,k,a[1000005],mark[1005];

bool ok()
{
    for(int i=1;i<=k;++i)
        if(!mark[i])
            return false;
    return true;
}

int solve()
{
    if(k<=3)
        return k;
    memset(mark,0,sizeof(mark));
    int head=0,tail,ans=INF;
    a[0]=1,a[1]=2,a[2]=3;
    mark[1]=mark[2]=mark[3]=1;
    for(tail=3;tail<n;++tail){
        a[tail]=(a[tail-1]+a[tail-2]+a[tail-3])%m+1;
        ++mark[a[tail]];
        while(head<=tail&&(a[head]<1||a[head]>k||mark[a[head]]>1))
            --mark[a[head++]];
        if(tail-head+1>=k&&tail-head+1<ans&&ok())
            ans=tail-head+1;
    }
    return ans;
}

int main()
{
    int T,cas=0;
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d%d",&n,&m,&k);
        printf("Case %d: ",++cas);
        if(n<k||k>m){
            printf("sequence nai\n");
            continue;
        }
        int ans=solve();
        if(ans==INF)
            printf("sequence nai\n");
        else
            printf("%d\n",ans);
    }
    return 0;
}