#include "sequence.h"
#include <bits/stdc++.h>
using namespace std;
#define inf 0x3F3F3F3F
struct DATA
{
int s1 = 0, s2 = 0, mxp1 = 0, mxp2 = 0, mxs1 = 0, mxs2 = 0, mnp1 = 0, mnp2 = 0, mns1 = 0, mns2 = 0;
};
const int MXN = 5e5 + 5;
const int B = 800;
DATA st[MXN << 2];
set<array<int, 2>> stmx[MXN << 4];
DATA combine(DATA x, DATA y)
{
return {
x.s1 + y.s1,
x.s2 + y.s2,
max(x.mxp1, x.s1 + y.mxp1),
max(x.mxp2, x.s2 + y.mxp2),
max(y.mxs1, y.s1 + x.mxs1),
max(y.mxs2, y.s2 + x.mxs2),
min(x.mnp1, x.s1 + y.mnp1),
min(x.mnp2, x.s2 + y.mnp2),
min(y.mns1, y.s1 + x.mns1),
min(y.mns2, y.s2 + x.mns2),
};
}
void upd(int l, int r, int x, int ind, int val)
{
if (l == r)
{
if (val != 0) st[x] = {val, val, max(0, val), max(0, val), max(0, val), max(0, val), min(0, val), min(0, val), min(0, val), min(0, val)};
else st[x] = {1, -1, 1, 0, 1, 0, 0, -1, 0, -1};
return;
}
int mid = (l + r) >> 1;
if (ind <= mid) upd(l, mid, 2*x, ind, val);
else upd(mid + 1, r, 2*x + 1, ind, val);
st[x] = combine(st[2*x], st[2*x + 1]);
}
DATA get(int l, int r, int x, int lx, int rx)
{
if (lx > rx)
{
return {0, 0, 0, 0, 0, 0, 0, 0, 0};
}
if (l > rx || r < lx) return {0, 0, 0, 0, 0, 0, 0, 0, 0};
if (l >= lx && r <= rx) return st[x];
int mid = (l + r) >> 1;
return combine(get(l, mid, 2*x, lx, rx), get(mid + 1, r, 2*x + 1, lx, rx));
}
int sequence(int N, vector<int> A)
{
vector<int> idx[N + 1];
for (int i = 0; i < N; i++) idx[A[i]].push_back(i);
for (int i = 0; i < N; i++) upd(0, N - 1, 1, i, 1);
int res = 1;
for (int val = 1; val <= N; val++)
{
vector<int> &v = idx[val];
for (int &i : v) upd(0, N - 1, 1, i, 0);
for (int r = 0, l = 0; r < v.size(); r++)
{
while (l <= r)
{
DATA x = get(0, N - 1, 1, v[l], v[r]);
// A = a, B = x - y
int A = r - l + 1;
int B = x.s1 - A;
DATA L = get(0, N - 1, 1, 0, v[l] - 1);
DATA R = get(0, N - 1, 1, v[r] + 1, N - 1);
int mn = B + L.mns2 + R.mnp2, mx = B + L.mxs1 + R.mxp1;
if ((mn <= 0 && 0 <= mx) || min(abs(mn), abs(mx)) <= A)
{
res = max(res, A);
break;
}
l++;
}
}
for (int &i : v) upd(0, N - 1, 1, i, -1);
}
return res;
}
