poj3261 Milk Patterns

#include<cstdio>
#include<algorithm>
using namespace std;
#define N 20050
int n,m,a[N];
int rank[N],tr[N],sa[N],hs[1000005],h[N];
struct node
{
    int x,id;
}nd[N];
bool vmp(node a,node b)
{
    return a.x<b.x;
}
bool cmp(int x,int y,int k)
{
    if(x+k>n||y+k>n)return 0;
    return rank[x]==rank[y]&&rank[x+k]==rank[y+k];
}
void get_sa()
{
    int i,cnt=0;
    for(i=1;i<=n;i++)hs[a[i]]++;
    for(i=1;i<=n;i++)if(hs[i])tr[i]=++cnt;
    for(i=1;i<=n;i++)hs[i]+=hs[i-1];
    for(i=n;i>=1;i--)rank[i]=tr[a[i]],sa[hs[a[i]]--]=i;
    for(int k=1;cnt!=n;k<<=1)
    {
        for(i=1;i<=n;i++)hs[i]=0;
        for(i=1;i<=n;i++)hs[rank[i]]++;
        for(i=1;i<=n;i++)hs[i]+=hs[i-1];
        for(i=n;i>=1;i--)if(sa[i]>k)tr[sa[i]-k]=hs[rank[sa[i]-k]]--;
        for(i=1;i<=k;i++)tr[n-i+1]=hs[rank[n-i+1]]--;
        for(i=1;i<=n;i++)sa[tr[i]]=i;
        for(i=1,cnt=0;i<=n;i++)tr[sa[i]]=cmp(sa[i],sa[i-1],k)?cnt:++cnt;
        for(i=1;i<=n;i++)rank[i]=tr[i];
    }
}
int f[N][18];
void get_h()
{
    for(int i=1;i<=n;i++)
    {
        if(rank[i]==1)continue;
        for(int j=max(1,h[rank[i-1]]-1);;j++)
        {
            if(a[i+j-1]==a[sa[rank[i]-1]+j-1])h[rank[i]]=j;
            else break;
        }
        f[rank[i]][0]=h[rank[i]];
    }
}
int main()
{
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)
        scanf("%d",&nd[i].x),nd[i].id=i;
    sort(nd+1,nd+1+n,vmp);
    int las = -1,cnt = 0;
    for(int i=1;i<=n;i++)
    {
        if(nd[i].x!=las)
        {
            las = nd[i].x;
            cnt++;
        }
        a[nd[i].id]=cnt;
    }
    m--;
    get_sa();
    get_h();
    int lg = -1,u=m;
    while(u)
    {
        lg++;
        u>>=1;
    }
    for(int i=1;i<=lg;i++)
    {
        for(int j=1;j<=n;j++)
        {
            f[j][i]=min(f[j][i-1],f[j+(1<<(i-1))][i-1]);
        }
    }
    int ans = -0x7fffffff;
    for(int i=1;i+m-1<=n;i++)
    {
        ans=max(ans,min(f[i][lg],f[i+m-(1<<lg)][lg]));
    }
    printf("%d\n",ans);
    return 0;
}