(Relax 后缀数组1.1)POJ 1743 Musical Theme(后缀数组的基本使用)

/*
 * POJ_1743.cpp
 *
 *  Created on: 2013年11月24日
 *      Author: Administrator
 */


#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>


using namespace std;

const int maxn = 20010;
struct node{
	int now;
	int next;
}d[maxn];

int val[maxn][2];
int c[maxn];
int rank[maxn];
int sa[maxn];
int pos[maxn];
int x[maxn];
int n;

int h[maxn];
int height[maxn];

void add_value(int u, int v, int i) {
	d[i].next = c[u];
	c[u] = i;
	d[i].now = v;
}

void radix_sort(int l, int r) {
	for(int k = 1 ; k >= 0 ; --k){

		memset(c, 0, sizeof(c));
		for(int i = r ; i >= l ; --i){
			add_value(val[pos[i]][k], pos[i], i);
		}
		int t = 0;
		for(int i = 0 ; i <= 20000 ; ++i){
			for (int j = c[i]; j; j = d[j].next){
				pos[++t] = d[j].now;
			}
		}
	}
	int t = 0;
	for(int i = 1 ; i <= n ; ++i){
		if (val[pos[i]][0] != val[pos[i - 1]][0]|| val[pos[i]][1] != val[pos[i - 1]][1]){
			t++;
		}
		rank[pos[i]] = t;
	}
}

bool exist(int len) {
	int Min = n + 1, Max = 0;
	for(int i = 1 ; i <= n ; ++i){
		if (height[i] < len) {
			if (Max - Min >= len){
				return 1;
			}
			Min = Max = sa[i];
		} else {
			Min = min(Min, sa[i]);
			Max = max(Max, sa[i]);
		}
	}
	if (Max - Min >= len)
		return 1;
	return 0;
}



void get_suffix_array() {
	int t = 1;
	while (t / 2 <= n) {
		for(int i = 1 ; i <= n ; ++i){

			val[i][0] = rank[i];
			val[i][1] = (((i + t / 2 <= n) ? rank[i + t / 2] : 0));
			pos[i] = i;
		}
		radix_sort(1, n);
		t *= 2;
	}
	for(int i = 1 ; i <= n ; ++i){
		sa[rank[i]] = i;
	}
}



void get_common_prefix() {
	memset(h, 0, sizeof(h));
	for(int i = 1 ; i <= n ; ++i){

		if (rank[i] == 1){
			h[i] = 0;
		}
		else {
			int now = 0;
			if (i > 1 && h[i - 1] > 1){
				now = h[i - 1] - 1;
			}
			while (now + i <= n && now + sa[rank[i] - 1] <= n&& x[now + i] == x[now + sa[rank[i] - 1]]){
				now++;
			}
			h[i] = now;
		}
	}
	for(int i = 1 ; i <= n ; ++i){
		height[rank[i]] = h[i];
	}
}




int binary_search(int l, int r) {
	while (l <= r) {
		int mid = (l + r) / 2;
		if (exist(mid)){
			l = mid + 1;
		}else{
			r = mid - 1;
		}
	}
	return r;
}

void solve() {
	for(int i = 1 ; i <= n-1 ; ++i){
		rank[i] = x[i] = x[i + 1] - x[i] + 88;
	}
	n--;
	get_suffix_array();
	get_common_prefix();
	int ans = binary_search(0, n) + 1;
	ans = ((ans < 5) ? 0 : ans);
	printf("%d\n", ans);
}

int main(){
	while(scanf("%d",&n)!=EOF,n){
		int i;
		for(i = 1 ; i <= n ; ++i){
			scanf("%d",&x[i]);
		}

		solve();
	}

	return 0;
}