Poj 3261 后缀数组

后缀数组真是强大，5s的题花了32ms

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn=20500;
int s[maxn], s1[maxn];
int id[maxn];
int sa[maxn], t[maxn], t2[maxn], c[maxn], n, tim;
int Rank[maxn], height[maxn];
void build_sa(int m, int n){
    int i, *x=t, *y=t2;
    for(i=0;i<m;i++)c[i]=0;
    for(i=0;i<n;i++)c[x[i]=s[i]]++;
    for(i=1;i<m;i++)c[i]+=c[i-1];
    for(i=n-1;i>=0;i--)sa[--c[x[i]]]=i;
    for(int k=1;k<=n;k<<=1){
        int p=0;
        for(i=n-k;i<n;i++)y[p++]=i;
        for(i=0;i<n;i++)if(sa[i]>=k)y[p++]=sa[i]-k;
        for(i=0;i<m;i++)c[i]=0;
        for(i=0;i<n;i++)c[x[y[i]]]++;
        for(i=1;i<m;i++)c[i]+=c[i-1];
        for(i=n-1;i>=0;i--)sa[--c[x[y[i]]]]=y[i];
        swap(x, y);
        p=1;x[sa[0]]=0;
        for(i=1;i<n;i++)
            x[sa[i]]=y[sa[i-1]]==y[sa[i]]&&y[sa[i-1]+k]==y[sa[i]+k]?p-1:p++;
        if(p>=n)break;
        m=p;
    }
}
void geth(int n){
    int i, j, k=0;
    for(i=0;i<n;i++)Rank[sa[i]]=i;
    for(i=0;i<n;i++){
        if(k)k--;
        if(Rank[i]==0)break;
        j=sa[Rank[i]-1];
        while(s[i+k]==s[j+k])k++;
        height[Rank[i]]=k;
    }
}
bool check(int mid, int n){
    int i;
    int st=0;
    for(i=1;i<n;i++){
        if(height[i]<mid){
            if(i-st>=tim)return true;
            st=i;
        }
    }
    if(n-st>=tim)return true;
    return false;
}
bool cmp(int x, int y){
    return s[x]<s[y];
}
int main()
{
    while(~scanf("%d%d", &n, &tim)){
        for(int i=0;i<n;i++)scanf("%d", &s[i]);
        for(int i=0;i<n;i++)id[i]=i;
        sort(id, id+n, cmp);
        int p=0;
        s1[id[0]]=++p;
        for(int i=1;i<n;i++)s1[id[i]]=s[id[i]]==s[id[i-1]]?p:++p;
        s1[n++]=0;
        swap(s1, s);
        build_sa(20005, n);
        geth(n);
        int l=1, r=n, ans=0;
        while(l<=r){
            if(r-l<=1){
                if(check(r, n))ans=r;
                else ans=l;
                break;
            }
            int mid=(l+r)/2;
            if(check(mid, n))l=mid;
            else r=mid;
        }
        printf("%d\n", ans);
    }
}