1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
// clang-format off
#include<bits/stdc++.h>
using namespace std;
using LL=long long;
#define FOR(i,l,r) for(auto i=(l);i<=(r);++i)
#define REP(i,n) FOR(i,0,(n)-1)
#define ssize(x) int(x.size())
auto operator<<(ostream&o,auto p)->decltype(p.first,o){return o<<"("<<p.first<<", "<<p.second<<")";}
auto operator<<(ostream&o,auto x)->decltype(x.end(),o){o<<"{";int i=0;for(auto e:x)o<<(", ")+2*!i++<<e;return o<<"}";}
#ifdef DEBUG
#define debug(x...) cerr<<"["#x"]: ",[](auto...$){((cerr<<$<<"; "),...);}(x),cerr<<'\n'
#else
#define debug(...) {}
#endif
// clang-format on

class RTree
{
    int base = 1;
    vector<int> data;

   public:
    RTree(int n)
    {
        while (base <= n) base <<= 1;
        data.resize(base << 1);
    };
    void set_atp(int i, int val)
    {
        data[i + base] = val;
        for (int v = (i + base) / 2; v > 0; v >>= 1)
            data[v] = max(data[v << 1], data[(v << 1) + 1]);
    }
    int max_onr(int l, int r)
    {
        int res = 0;
        l += base, r += base;
        while (l <= r) {
            if (l & 1) res = max(res, data[l++]);
            if (!(r & 1)) res = max(res, data[r--]);
            l >>= 1, r >>= 1;
        }
        return res;
    }
};

int N, max_val = 0;
vector<int> seq;
vector<int> rst;  // greatest i <= n s.t. dp[i - 1] >= dp[n]

void
calc_range_start()
{
    rst.resize(N, 0);
    RTree last(max_val + 1);  // last index+1 per value
    REP (n, N) {
        rst[n] = last.max_onr(seq[n], max_val);
        last.set_atp(seq[n], n + 1);
    }
    debug(rst);
}

int
dp_brute()
{
    RTree dp(N);
    REP (n, N) {
        int val = dp.max_onr(rst[n], n - 1) + 1;
        dp.set_atp(n, val);
    }
    return dp.max_onr(0, N - 1);
}

int
main()
{
    cin.tie(0)->sync_with_stdio(0);
    cin >> N;
    seq.reserve(N + N);
    seq.resize(N);
    for (auto &x : seq) cin >> x;
    max_val = *max_element(seq.begin(), seq.end());
    REP (i, N) seq.emplace_back(seq[i]);
    debug(seq);
    N += N;

    calc_range_start();
    cout << dp_brute() << "\n";
    return 0;
}