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
#include <bits/stdc++.h>
using namespace std;

constexpr int N = 50005;
int a[N], b[N];

int main () {
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);

	int n;
	cin >> n;
	for (int i = 1; i <= n; i++) {
		cin >> a[i];
		b[i] = a[i];
	}

	int x = 0, y = 0;
	for (int i = 1; i < n; i++) {
		if (i%2==1) {
			if (a[i] >= a[i+1]) {
				x++;
				a[i+1] = 100000000;
			}
		}
		else {
			if (a[i] <= a[i+1]) {
				x++;
				a[i+1] = -100000000;
			}
		}
	}
	for (int i = 1; i < n; i++) {
		if (i%2==0) {
			if (b[i] >= b[i+1]) {
				y++;
				b[i+1] = 100000000;
			}
		}
		else {
			if (b[i] <= b[i+1]) {
				y++;
				b[i+1] = -100000000;
			}
		}
	}
	
	cout << min(x, y);

	return 0;
}