uva 12206 - Stammering Aliens

基于hash的LCP算法；

#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 40010
using namespace std;

const int x=123;
int n,m,pos;
unsigned long long h[maxn],xp[maxn],hash[maxn];
int rank[maxn];

bool cmp(const int &a,const int &b)
{
    return hash[a]<hash[b]||hash[a]==hash[b]&&a<b;
}

int possible(int l)
{
    int c=0;
    pos=-1;
    for(int i=0;i<n-l+1;i++)
    {
        rank[i]=i;
        hash[i]=h[i]-h[i+l]*xp[l];
    }
    sort(rank,rank+n-l+1,cmp);
    for(int i=0;i<n-l+1;i++)
    {
        if(i==0||hash[rank[i]]!=hash[rank[i-1]])c=0;
        if(++c>=m)pos=max(pos,rank[i]);
    }
    return pos>=0;
}

int main()
{
    char s[maxn];
    while(scanf("%d",&m)&&m)
    {
        scanf("%s",s);
        n=strlen(s);
        h[n]=0;
        for(int i=n-1;i>=0;i--)
            h[i]=h[i+1]*x+(s[i]-'a');
        xp[0]=1;
        for(int i=1;i<=n;i++)xp[i]=xp[i-1]*x;
        if(!possible(1))puts("none");
        else
        {
            int l=1,r=n+1;
            while(l+1<r)
            {
                int mid=(r+l)>>1;
                if(possible(mid))l=mid;
                else r=mid;
            }
            possible(l);
            printf("%d %d\n",l,pos);
        }
    }
    return 0;
}