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