G - Local Extrema
You are given an array a. Some element of this array ai is a local minimum iff it is strictly less than both of its neighbours (that is, ai < ai - 1 and ai < ai + 1). Also the element can be called local maximum iff it is strictly greater than its neighbours (that is, ai > ai - 1 and ai > ai + 1). Since a1 and an have only one neighbour each, they are neither local minima nor local maxima.
An element is called a local extremum iff it is either local maximum or local minimum. Your task is to calculate the number of local extrema in the given array.
Input
The first line contains one integer n (1 ≤ n ≤ 1000) — the number of elements in array a.
The second line contains n integers a1, a2, …, an (1 ≤ ai ≤ 1000) — the elements of array a.
Output
Print the number of local extrema in the given array.
Examples
Input
3
1 2 3
Output
0
Input
4
1 5 2 5
Output
2
思路
從a[1]到a[n-2]來一次循環，判斷a[i]是否是a[i-1]和a[i+1]中的最大或最小值就行了。
代碼
#include <stdio.h>
int main()
{
int n;
scanf("%d",&n);
int a[n];
for(int i=0;i<n;i++)
scanf("%d",&a[i]);
int min=0,max=0;
for(int i=1;i<=n-2;i++){
if(a[i]<a[i-1]&&a[i]<a[i+1])
min++;
else if(a[i]>a[i+1]&&a[i]>a[i-1])
max++;
}
printf("%d",min+max);
return 0;
}