UVa 12206 (字符串哈希) Stammering Aliens

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 using namespace std;
 5 
 6 const int maxn = 40000 + 10;
 7 const int x = 123;
 8 int n, m, pos;
 9 unsigned long long H[maxn], xp[maxn];
10 unsigned long long hash[maxn];
11 int rank[maxn];
12 char s[maxn];
13 
14 bool cmp(const int& a, const int& b)
15 { return hash[a] < hash[b] || (hash[a] == hash[b] && a < b); }
16 
17 bool possible(int L)
18 {
19     int cnt = 0;
20     pos = -1;
21     for(int i = 0; i + L - 1 < n; i++)
22     {
23         rank[i] = i;
24         hash[i] = H[i] - H[i + L] * xp[L];
25     }
26     sort(rank, rank + n - L + 1, cmp);
27     for(int i = 0; i + L - 1 < n; i++)
28     {
29         if(i == 0 || hash[rank[i]] != hash[rank[i - 1]]) cnt = 0;
30         if(++cnt >= m) pos = max(pos, rank[i]);
31     }
32     return pos >= 0;
33 }
34 
35 int main()
36 {
37     //freopen("in.txt", "r", stdin);
38 
39     xp[0] = 1;
40     for(int i = 1; i < maxn; i++) xp[i] = xp[i - 1] * x;
41 
42     while(scanf("%d", &m) == 1 && m)
43     {
44         scanf("%s", s);
45         n = strlen(s);
46         H[n] = 0;
47         for(int i = n - 1; i >= 0; i--) H[i] = H[i + 1] * x + s[i] - ‘a‘;
48 
49         if(!possible(1)) puts("none");
50         else
51         {
52             int L = 1, R = n;
53             while(L < R)
54             {
55                 int M = (L + R + 1) / 2;
56                 if(possible(M)) L = M;
57                 else R = M - 1;
58             }
59             possible(L);
60             printf("%d %d\n", L, pos);
61         }
62     }
63 
64     return 0;
65 }