#Monotonic function

0 0 0 0 0 1 1 1 1

Bitonic function

For example, first increases (reaches to a maximum) and then decreases

11 15 16 4 3 1 (Max value is 16) ? /\

Standard template

#include <bits/stdc++.h>

using namespace std;

int n;
int arr[10005];

int check(int x) {
     // return a[x] > a; // Upper bound (smallest number strictly greater than 'a') 
     // return a[x] >= a; // Lower bound (smallest number greater than or equal to 'a') 
     return 1;
}

void solve() {
    cin >> n;
    for (int i = 0; i < n; i++) {
        cin >> arr[i];
    }

    int low = 0;
    int high = n - 1;
    
    int ans = 0; // ##
    while (low <= high) {    
        int mid = (low + high) / 2;
        if (check(mid)) {        
            ans = mid;
            high = mid - 1; // First occurance of
        } else {        
            low = mid + 1;
        }
    }
    cout << ans << endl;
}