#include <bits/stdc++.h>
using namespace std;
const int R = 1 << 19;
int mn[R * 2], mx[R * 2], psh[R * 2];
void push(int node) {
if (psh[node] != 0) {
mn[node * 2] += psh[node];
mx[node * 2] += psh[node];
psh[node * 2] += psh[node];
mn[node * 2 + 1] += psh[node];
mx[node * 2 + 1] += psh[node];
psh[node * 2 + 1] += psh[node];
}
psh[node] = 0;
}
void add(int ql, int qr, int val, int node = 1, int nl = 0, int nr = R) {
if (ql <= nl && nr <= qr) {
mn[node] += val;
mx[node] += val;
psh[node] += val;
return;
}
if (qr <= nl || nr <= ql) {
return;
}
push(node);
int nm = (nl + nr) / 2;
add(ql, qr, val, node * 2, nl, nm);
add(ql, qr, val, node * 2 + 1, nm, nr);
mn[node] = min(mn[node * 2], mn[node * 2 + 1]);
mx[node] = max(mx[node * 2], mx[node * 2 + 1]);
}
pair<int, int> get(int ql, int qr, int node = 1, int nl = 0, int nr = R) {
if (ql <= nl && nr <= qr) {
return {mn[node], mx[node]};
}
if (qr <= nl || nr <= ql) {
return {R, -R};
}
push(node);
int nm = (nl + nr) / 2;
auto p1 = get(ql, qr, node * 2, nl, nm), p2 = get(ql, qr, node * 2 + 1, nm, nr);
mn[node] = min(mn[node * 2], mn[node * 2 + 1]);
mx[node] = max(mx[node * 2], mx[node * 2 + 1]);
return {min(p1.first, p2.first), max(p1.second, p2.second)};
}
int sequence(int n, vector<int> a) {
vector<vector<int>> pos(n);
for (int i = 0; i < n; ++i) {
a[i]--;
pos[a[i]].push_back(i);
}
for (int i = 0; i < n; ++i) {
add(i + 1, n + 1, 1);
}
int ans = 1;
vector<int> pr_min1(n), pr_min2(n), pr_max1(n), pr_max2(n), suf_min1(n), suf_min2(n), suf_max1(n), suf_max2(n);
for (int vl = 0; vl < n; ++vl) {
for (int i = 0; i < (int)pos[vl].size(); ++i) {
auto p = get(0, pos[vl][i] + 1);
pr_min1[i] = p.first;
pr_max1[i] = p.second;
p = get(pos[vl][i] + 1, n + 1);
suf_min1[i] = p.first;
suf_max1[i] = p.second;
}
for (auto p : pos[vl]) {
add(p + 1, n + 1, -2);
}
for (int i = 0; i < (int)pos[vl].size(); ++i) {
auto p = get(0, pos[vl][i] + 1);
pr_min2[i] = p.first;
pr_max2[i] = p.second;
p = get(pos[vl][i] + 1, n + 1);
suf_min2[i] = p.first;
suf_max2[i] = p.second;
}
int l = 1, r = pos[vl].size() + 1;
while (l < r - 1) {
int m = (l + r) / 2;
bool check = false;
for (int i = 0; i + m <= (int)pos[vl].size(); ++i) {
if (pr_min1[i] <= suf_max1[i + m - 1] && suf_min1[i + m - 1] <= pr_max1[i]) {
check = true;
} else if (pr_min2[i] <= suf_max2[i + m - 1] && suf_min2[i + m - 1] <= pr_max2[i]) {
check = true;
} else if (pr_max1[i] <= suf_min1[i + m - 1] && suf_max2[i + m - 1] <= pr_min2[i]) {
check = true;
} else if (suf_max1[i] <= pr_min1[i + m - 1] && pr_max2[i + m - 1] <= suf_min2[i]) {
check = true;
}
}
if (check) {
l = m;
} else {
r = m;
}
}
ans = max(ans, l);
}
return ans;
}
