【后缀数组】 POJ 1743 Musical Theme

#include <iostream>
#include <sstream>
#include <algorithm>
#include <vector>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <bitset>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <climits>
#define maxn 20005
#define eps 1e-6
#define mod 10007
#define INF 99999999
#define lowbit(x) (x&(-x))
//#define lson o<<1, L, mid
//#define rson o<<1 | 1, mid+1, R
typedef long long LL;
using namespace std;

int s[maxn];
int t[maxn], t2[maxn], c[maxn], sa[maxn];
void build(int n, int m)
{
int i, k, p, *x = t, *y = t2;
for(i = 0; i < m; i++) c[i] = 0;
for(i = 0; i < n; i++) c[x[i] = s[i]]++;
for(i = 1; i < m; i++) c[i] += c[i-1];
for(i = n-1; i >= 0; i--) sa[--c[x[i]]] = i;
for(k = 1; k <= n; k<<=1) {
p = 0;
for(i = n-k; i < n; i++) y[p++] = i;
for(i = 0; i < n; i++) if(sa[i] >= k) y[p++] = sa[i] - k;
for(i = 0; i < m; i++) c[i] = 0;
for(i = 0; i < n; i++) c[x[y[i]]]++;
for(i = 1; i < m; i++) c[i] += c[i-1];
for(i = n-1; i >= 0; i--) sa[--c[x[y[i]]]] = y[i];
swap(x, y), p = 1, x[sa[0]] = 0;
for(i = 1; i < n; i++)
x[sa[i]] = y[sa[i]] == y[sa[i-1]] && y[sa[i]+k] == y[sa[i-1]+k] ? p-1 : p++;
if(p >= n) break;
m = p;
}
}
int rank[maxn], height[maxn];
void getheight(int n)
{
int i, j, k = 0;
for(i = 0; i <= n; i++) rank[sa[i]] = i;
for(i = 0; i < n; i++) {
if(k) k--;
j = sa[rank[i]-1];
while(s[i+k] == s[j+k]) k++;
height[rank[i]] = k;
}
}
bool is(int p, int n)
{
int i, _max = 0, _min = INF;
for(i = 1; i <= n; i++) {
if(height[i] >= p) {
_max = max(_max, sa[i]);
_min = min(_min, sa[i]);
_max = max(_max, sa[i-1]);
_min = min(_min, sa[i-1]);
}
else {
if(_max - _min > p) return true;
_max = 0;
_min = INF;
}
}
if(_max - _min > p) return true;
else return false;
}
int search(int n)
{
int bot = 0, top = 10000, mid, res = 0;
while(top >= bot) {
mid= (top+bot)>>1;
if(is(mid, n)) bot = mid+1, res = max(res, mid);
else top = mid-1;
}
return res;
}
int main(void)
{
int i, n, ans;
while(scanf("%d", &n), n!=0) {
for(i = 0; i < n; i++)
scanf("%d", &s[i]);
for(i = 0; i < n-1; i++)
s[i] = s[i+1] - s[i]+100;
s[i] = 0;
build(n, 200);
getheight(n-1);
ans = search(n-1);
if(ans >= 4) printf("%d\n", ans+1);
else printf("0\n");
}
return 0;
}