POJ 1743. Musical Theme

#include <iostream>
#include <cstring>
#include <cstdio>
const int N = 20000 + 7;
using namespace std;
int n,r[N],wb[N],wss[N],wv[N],sa[N],rank[N],li[N];

int cmp(int *r,int a,int b,int l)
{
    return r[a] == r[b] && r[a+l] == r[b+l];
}

void Da(int n,int m)
{
    int i,j,p,*x = rank, *y = wb, *t;
    for(i = 0; i < m; ++i) wss[i] = 0;
    for(i = 0; i < n; ++i) ++wss[x[i]=r[i]];
    for(i = 1; i < m; ++i) wss[i] += wss[i-1];
    for(i = n-1; i >= 0; --i ) sa[--wss[x[i]]] = i;
    for(j = p = 1; p < n; j <<= 1, m = p)
    {
        for(p = 0,i = n-j; i < n; ++i) y[p++] = i;
        for(i = 0; i < n; ++i) if(sa[i] >= j) y[p++] = sa[i] - j;
        for(i = 0; i < n; ++i) wv[i] = x[y[i]];
        for(i = 0; i < m; ++i) wss[i] = 0;
        for(i = 0; i < n; ++i) ++wss[wv[i]];
        for(i = 1; i < m; ++i) wss[i] += wss[i-1];
        for(i = n-1; i >= 0; --i) sa[--wss[wv[i]]] = y[i];
        for(t = x, x = y, y = t, p = i = 1, x[sa[0]] = 0; i < n; ++i)
        x[sa[i]] = cmp(y,sa[i-1],sa[i],j)?p-1:p++;
    }
}

int f[N], hi[N];
void cal_height( )
{
    int i,j,k = 0;
    for(i = 1; i <= n; ++i) f[sa[i]] = i;
    for(i = 0; i < n; hi[f[i++]] = k)
    for(k?k--:0,j = sa[f[i]-1]; r[i+k] == r[j+k]; ++k);
}

bool check(int len)
{
    int minx = n + 1 , maxx = -1,i;
    for(i = 2; i <= n; ++i)
    {
        if(hi[i] >= len)
        {
            minx = min(minx,min(sa[i],sa[i-1]));
            maxx = max(maxx,max(sa[i],sa[i-1]));
        }
        else
        {
            if(minx + len < maxx) return true;
            minx = n + 1, maxx = -1;
         }
    }
    if(minx + len < maxx) return true; return false;
}

int  binary_search( )
{
    int L = 1, R =  ( n >> 1 )+ 1, mid, ret = -1;
    while(L <= R)
    {
        mid = ( L + R ) >> 1;
        if(check(mid)) L = mid + 1, ret = max(ret , mid);
        else R = mid - 1;
    }
    return ret;
}

int main()
{
    while(~scanf("%d",&n) && n)
    {
        int i; memset(r,0,sizeof(r));
        for(i = 0; i < n; ++i) scanf("%d",r+i);
        for(i = 0; i < n; ++i) r[i] = r[i+1] - r[i] + 100; ; n--; r[n] = 0;
        Da(n+1,201);
        cal_height( );
        int ans = binary_search()+1;
        if( ans < 5) puts("0");
        else printf("%d\n",ans);
    }
    return 0;
}