后缀数组【倍增计数排序求sa】poj1743

#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#define maxn 25001
using namespace std;

int wa[maxn], wb[maxn], wv[maxn], ws[maxn];
int cmp(int *r, int a, int b, int l)
{return r[a] == r[b] && r[a + l] == r[b + l];}

void da(int *r, int *sa, int n, int m)
{
int i, j, p, *x = wa, *y = wb, *t;
for (i = 0; i < m; i++) ws[i] = 0;
for (i = 0; i < n; i++) ws[x[i] = r[i]]++;
for (i = 1; i < m; i++) ws[i] += ws[i - 1];
for (i = n - 1; i >= 0; i--) sa[--ws[x[i]]] = i;
for (j = 1, p = 1; p < n; j *= 2, 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++) ws[i] = 0;
for (i = 0; i < n; i++) ws[wv[i]]++;
for (i = 1; i < m; i++) ws[i] += ws[i - 1];
for (i = n - 1; i >= 0; i--) sa[--ws[wv[i]]] = y[i];
for (t = x, x = y, y = t, p = 1, x[sa[0]] = 0, i = 1; i < n; i++)
x[sa[i]] = cmp(y, sa[i - 1], sa[i], j) ? p - 1 : p++;
}
return;
}
int rank[maxn], height[maxn];
void calheight(int *r, int *sa, int n)
{
int i, j, k = 0;
for (i = 1; i <= n; i++) rank[sa[i]] = i;
for (i = 0; i < n; height[rank[i++]] = k)
for (k ? k-- : 0, j = sa[rank[i] - 1]; r[i + k] == r[j + k]; k++);
return;
}
int RMQ[maxn];
int mm[maxn];
int best[20][maxn];
void initRMQ(int n)
{
int i, j, a, b;
for (mm[0] = -1, i = 1; i <= n; i++)
mm[i] = ((i & (i - 1)) == 0) ? mm[i - 1] + 1 : mm[i - 1];
for (i = 1; i <= n; i++) best[0][i] = i;
for (i = 1; i <= mm
; i++)
for (j = 1; j <= n + 1 - (1 << i); j++)
{
a = best[i - 1][j];
b = best[i - 1][j + (1 << (i - 1))];
if (RMQ[a] < RMQ[b]) best[i][j] = a;
else best[i][j] = b;
}
return;
}
int askRMQ(int a, int b)
{
int t;
t = mm[b - a + 1]; b -= (1 << t) - 1;
a = best[t][a]; b = best[t][b];
return RMQ[a] < RMQ[b] ? a : b;
}
int lcp(int a, int b)
{
int t;
a = rank[a]; b = rank[b];
if (a > b) {t = a; a = b; b = t;}
return (height[askRMQ(a + 1, b)]);
}
int num[maxn], n;
int sa[maxn];

bool check(int k) {
int Min = ~0u >> 1, Max = 0;
int ans = 0;
for (int i = 2; i <=n; i++)
{
if (height[i] < k)
{
ans = max(ans, Max - Min);
Min = n; Max = 0;
continue;
}
if (height[i - 1] < k)
{
Min = min(Min, sa[i - 1]);
Max = max(Max, sa[i - 1]);
}
if (height[i]>=k)
{
Min = min(Min, sa[i]);
Max = max(Max, sa[i]);
}
}
ans = max(ans, Max - Min);
if (ans >= k)
return 1;
return 0;
}

int doit() {

int t = 1, w = n;
while (w - t > 1)
{
int mid = (t + w) / 2;
if (check(mid))
t = mid;
else
w = mid;
}
if (check(w))
return w;
if (check(t))
return t;
return 0;
}

int main() {
for (;;)
{
scanf("%d", &n);
if (!n)
break;
for (int i = 0; i < n; i++)
scanf("%d", &num[i]);
for (int i = 0; i < n - 1; i++)
num[i] = num[i + 1] - num[i] + 90;
if (n < 10)
{
puts("0");
continue;
}
num[--n] = 0;
da(num, sa, n + 1, 300);
calheight(num, sa, n);
int tmp = doit();
if (tmp < 4)
printf("0\n");
else
printf("%d\n", tmp + 1);
}
}