poj1743 Musical Theme

 1 #include <cstdlib>
 2 #include <cstring>
 3 #include <cstdio>
 4 #include <algorithm>
 5 
 6 const int N = 20005;
 7 int sa[N],s[N],wa[N], wb[N], ws[N], wv[N];
 8 int rank[N], height[N];
 9 
10 bool cmp(int r[], int a, int b, int l)
11 {
12     return r[a] == r[b] && r[a+l] == r[b+l];
13 }
14 
15 void da(int r[], int sa[], int n, int m)
16 {
17     int i, j, p, *x = wa, *y = wb;
18     for (i = 0; i < m; ++i) ws[i] = 0;
19     for (i = 0; i < n; ++i) ws[x[i]=r[i]]++;
20     for (i = 1; i < m; ++i) ws[i] += ws[i-1];
21     for (i = n-1; i >= 0; --i) sa[--ws[x[i]]] = i;
22     for (j = 1, p = 1; p < n; j *= 2, m = p)
23     {
24         for (p = 0, i = n - j; i < n; ++i) y[p++] = i;
25         for (i = 0; i < n; ++i) if (sa[i] >= j) y[p++] = sa[i] - j;
26         for (i = 0; i < n; ++i) wv[i] = x[y[i]];
27         for (i = 0; i < m; ++i) ws[i] = 0;
28         for (i = 0; i < n; ++i) ws[wv[i]]++;
29         for (i = 1; i < m; ++i) ws[i] += ws[i-1];
30         for (i = n-1; i >= 0; --i) sa[--ws[wv[i]]] = y[i];
31         for (std::swap(x, y), p = 1, x[sa[0]] = 0, i = 1; i < n; ++i)
32             x[sa[i]] = cmp(y, sa[i-1], sa[i], j) ? p-1 : p++;
33     }
34 }
35 
36 void calheight(int r[], int sa[], int n)
37 {
38     int i, j, k = 0;
39     for (i = 1; i <= n; ++i) rank[sa[i]] = i;
40     for (i = 0; i < n; height[rank[i++]] = k)
41         for (k?k--:0, j = sa[rank[i]-1]; r[i+k] == r[j+k]; k++);
42 }
43 bool check(int len,int x)
44 {
45     int mx=sa[1],mi=sa[1];
46     for(int i=2;i<=len;i++)
47     {
48         if(height[i]<x)
49         {
50             if(mx-mi>=x)
51                 return 1;
52             mx=mi=sa[i];
53         }
54         else
55         {
56             mx=std::max(sa[i],mx);
57             mi=std::min(sa[i],mi);
58         }
59     }
60     return mx-mi>=x;
61 }
62 int main()
63 {
64     int n;
65     while(scanf("%d",&n)&&n)
66     {
67         int x,ls,len=0;
68         scanf("%d",&ls);
69         for(int i=0;i<n-1;i++)
70             scanf("%d",&x),s[len++]=x-ls+100,ls=x;
71         s[len]=0;
72         da(s,sa,len+1,200);
73         calheight(s,sa,len);
74         int l=5,r=n/2,ans=0;
75         while(l<=r)
76         {
77             int mid=l+r>>1;
78             if(check(len,mid-1))
79                 ans=mid,l=mid+1;
80             else
81                 r=mid-1;
82         }
83         printf("%d\n",ans);
84     }
85     return 0;
86 }