POJ 1743 Musical Theme

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 using namespace std;
 5 const int maxn = 500010;
 6 int sa[maxn],rk[maxn],height[maxn],c[maxn];
 7 int n,t[maxn],t2[maxn],s[maxn];
 8 void build_sa(int m) {
 9     int i,j,*x = t,*y = t2;
10     for(i = 0; i < m; ++i) c[i] = 0;
11     for(i = 0; i < n; ++i) c[x[i] = s[i]]++;
12     for(i = 1; i < m; ++i) c[i] += c[i-1];
13     for(i = n-1; i >= 0; --i) sa[--c[x[i]]] = i;
14 
15     for(int k = 1; k <= n; k <<= 1) {
16         int p = 0;
17         for(i = 0; i < m; ++i) c[i] = 0;
18         for(i = n-k; i < n; ++i) y[p++] = i;
19         for(i = 0; i < n; ++i)
20             if(sa[i] >= k) y[p++] = sa[i] - k;
21         for(i = 0; i < n; ++i) c[x[y[i]]]++;
22         for(i = 1; i < m; ++i) c[i] += c[i-1];
23         for(i = n-1; i >= 0; --i) sa[--c[x[y[i]]]] = y[i];
24 
25         swap(x,y);
26         p = 1;
27         x[sa[0]] = 0;
28         for(i = 1; i < n; ++i)
29             if(y[sa[i]] == y[sa[i-1]] && y[sa[i]+k] == y[sa[i-1]+k])
30                 x[sa[i]] = p-1;
31             else x[sa[i]] = p++;
32         if(p >= n) break;
33         m = p;
34     }
35 }
36 void getHeight() {
37     int i,j,k = 0;
38     for(i = 0; i < n; ++i) rk[sa[i]] = i;
39     for(i = 0; i < n; ++i) {
40         if(k) --k;
41         j = sa[rk[i]-1];
42         while(i + k < n && j + k < n && s[i+k] == s[j+k]) k++;
43         height[rk[i]] = k;
44     }
45 }
46 bool check(int k) {
47     int low = sa[1],high = sa[1];
48     for(int i = 2; i < n; ++i) {
49         if(height[i] < k) low = high = sa[i];
50         else {
51             low = min(sa[i],low);
52             high = max(sa[i],high);
53             if(high - low > k) return true;
54         }
55     }
56     return false;
57 }
58 int tmp[maxn];
59 int main() {
60     while(scanf("%d",&n),n) {
61         for(int i = 0; i < n; ++i)
62             scanf("%d",tmp+i);
63         for(int i = 0; i+1 < n; ++i)
64             s[i] = tmp[i+1] - tmp[i] + 90;
65         s[n-1] = 0;
66         build_sa(200);
67         getHeight();
68         int low = 4,high = n,ret = -1;
69         while(low <= high) {
70             int mid = (low + high)>>1;
71             if(check(mid)) {
72                 low = mid + 1;
73                 ret = mid;
74             } else high = mid - 1;
75         }
76         printf("%d\n",ret+1);
77     }
78     return 0;
79 }