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
#include <bits/stdc++.h>

#define HILL 1000000000 
#define VALLEY -1000000000 

using namespace std;

void solve() {
    int n;
    cin >> n;
    vector<long long> a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];

    vector<long long> b(a);

    int ans = 0;
    int down = 0;
    int up = 0;
    int mode = 0; // 1 means current elem is a hill, 0 a valley

    mode = 1;
    for (int i = 1; i < n; i++) {
        if (mode == 1 && a[i - 1] >= a[i]) {
            a[i] = HILL;
            up++;
        } else if (mode == 0 && a[i - 1] <= a[i]) {
            a[i] = VALLEY;
            up++;
        }
        mode = 1 - mode;
    }

    a = b;

    mode = 0;
    for (int i = 1; i < n; i++) {
        if (mode == 1 && a[i - 1] >= a[i]) {
            a[i] = HILL;
            down++;
        } else if (mode == 0 && a[i - 1] <= a[i]) {
            a[i] = VALLEY;
            down++;
        }
        mode = 1 - mode;
    }

    ans = min(up, down);

    cout << ans << "\n";
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    
    solve();
  
    return 0;
}