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
// Daniel Grzegorzewski
// while (clock()<=69*CLOCKS_PER_SEC)
#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
// #pragma GCC optimize("Ofast")
// #pragma GCC target("avx,avx2,fma")

#define MP make_pair
#define PB push_back
#define ST first
#define ND second

using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

//X.find_by_order(k); - zwraca iterator na k-ty element (numeracja od zerowego)
//X.order_of_key(k); - zwraca liczbę elementów ostro mniejszych niż k

typedef pair<int, int> PII;
typedef vector<int> VI;
typedef vector<PII> VII;
typedef long long LL;

void init_ios() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
}

auto random_address = [] { char *p = new char; delete p; return uint64_t(p); };
 
const uint64_t SEED = chrono::steady_clock::now().time_since_epoch().count() * (random_address() | 1);
mt19937_64 rng(SEED);

const int N = 5*(int)1e4 + 3;

int n, a[N], dp[N][4];

int main() {
  init_ios();
  cin >> n;
  for (int i = 1; i <= n; ++i) {
    cin >> a[i];
    dp[i][0] = dp[i][1] = dp[i][2] = dp[i][3] = N;
  }
  dp[1][0] = dp[1][1] = 0;
  dp[1][2] = dp[1][3] = 1;
  for (int i = 2; i <= n; ++i) {
    if (a[i] > a[i-1])
      dp[i][1] = min({dp[i][1], dp[i-1][0], dp[i-1][2]});
    else if (a[i] < a[i-1])
      dp[i][0] = min({dp[i][0], dp[i-1][1], dp[i-1][3]});
    dp[i][0] = min(dp[i][0], dp[i-1][3]);
    dp[i][1] = min(dp[i][1], dp[i-1][2]);
    dp[i][2] = min(dp[i][2], 1+min(dp[i-1][1], dp[i-1][3]));
    dp[i][3] = min(dp[i][3], 1+min(dp[i-1][0], dp[i-1][2]));
  }
  cout<<min({dp[n][0], dp[n][1], dp[n][2], dp[n][3]})<<"\n";
}