acdream 1430 SETI 后缀数组+height分组

Posted 2020-10-02 llguanli

这题昨天比赛的时候逗了，后缀想不出来，由于n^2的T了，就没往后缀数组想……并且之后解题的人又说用二分套二分来做。然后就更不会了……

刚才看了题解，唉……原来题讲解n^2的也能够过，然后就……这样了！

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<map>
#include<queue>
#include<set>
#include<cmath>
#include<bitset>
#define mem(a,b) memset(a,b,sizeof(a))
#define lson i<<1,l,mid
#define rson i<<1|1,mid+1,r
#define llson j<<1,l,mid
#define rrson j<<1|1,mid+1,r
#define INF 0x7fffffff
#define seed 13131
#define seed1 1313
#define maxn 20005
typedef long long ll;
typedef unsigned long long ull;
using namespace std;
void radix(int *str,int *a,int *b,int n,int m)
{
    static int count[maxn];
    mem(count,0);
    for(int i=0; i<n; i++) ++count[str[a[i]]];
    for(int i=1; i<=m; i++) count[i]+=count[i-1];
    for(int i=n-1; i>=0; i--) b[--count[str[a[i]]]]=a[i];
}
void suffix(int *str,int *sa,int n,int m) //倍增算法计算出后缀数组sa
{
    static int rank[maxn],a[maxn],b[maxn];
    for(int i=0; i<n; i++) rank[i]=i;
    radix(str,rank,sa,n,m);
    rank[sa[0]]=0;
    for(int i=1; i<n; i++)
        rank[sa[i]]=rank[sa[i-1]]+(str[sa[i]]!=str[sa[i-1]]);
    for(int i=0; 1<<i<n; i++)
    {
        for(int j=0; j<n; j++)
        {
            a[j]=rank[j]+1;
            b[j]=j+(1<<i)>=n?0:rank[j+(1<<i)]+1;
            sa[j]=j;
        }
        radix(b,sa,rank,n,n);
        radix(a,rank,sa,n,n);
        rank[sa[0]]=0;
        for(int j=1; j<n; j++)
            rank[sa[j]]=rank[sa[j-1]]+(a[sa[j-1]]!=a[sa[j]]||b[sa[j-1]]!=b[sa[j]]);
    }
}
void calcHeight(int *str,int *sa,int *h,int *rank,int n) //求出最长公共前缀数组h
{
    int k=0;
    h[0]=0;
    for(int i=0; i<n; i++) rank[sa[i]]=i;
    for(int i=0; i<n; i++)
    {
        k=k==0?0:k-1;
        if(rank[i])
            while(str[i+k]==str[sa[rank[i]-1]+k]) k++;
        else k=0;
        h[rank[i]]=k;
    }
}
int a[maxn],sa[maxn],height[maxn],rank[maxn];
char s[maxn];
int main()
{
    //freopen("1.txt","r",stdin);
    scanf("%s",s);
    int n=strlen(s);
    copy(s,s+n,a);
    suffix(a,sa,n,150);
    calcHeight(a,sa,height,rank,n);
    int Max,Min,sum=0;
    for(int i=1;i<=n/2;i++)
    {
        Max=Min=sa[0];
        for(int j=1;j<=n;j++)
        {
            if(height[j]<i||j==n)
            {
                if(Max-Min>=i) sum++;
                Max=Min=sa[j];
            }
            else
            {
                Max=max(Max,sa[j]);
                Min=min(Min,sa[j]);
            }
        }
    }
    printf("%d\n",sum);
    return 0;
}