uvalive 4513 Stammering Aliens

题意：给你一个串，问期中至少出现m次的最长子串及其起始位置的坐标。

思路：hash+LCP+二分答案

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;

 const int maxn =  + ;
 const int x = ;
 int n, m, pos;
 unsigned long long H[maxn], xp[maxn];

 unsigned long long hash[maxn];
 int rank[maxn];

 int 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())
             printf("none\n");
         else
         {
             int L = , R = n+;
             while(R - L > )
             {
                 int M = L + (R-L)/;
                 if(possible(M))
                     L = M;
                 else R = M;
             }
             possible(L);
             printf("%d %d\n", L, pos);
         }
     }
     return ;
 }