Find the maximum element in an array which is first increasing and then decreasing in C++

Suppose we have one array, which is initially increasing then decreasing. We have to find the max value in the array. So if the array elements are like A = [8, 10, 20, 80, 100, 250, 450, 100, 3, 2, 1], then output will be 500.

We can use the binary search to solve this. There are three conditions −

When mid is greater than both of its adjacent elements, then mid is maximum
If mid is greater than the next element, but smaller than previous element, then max lies on the left side of mid.
If mid element is smaller than the next element, but greater than previous element, then max lies on the right side of mid.

Example

Live Demo

#include<iostream>
using namespace std;
int getMaxElement(int array[], int left, int right) {
   if (left == right)
      return array[left];
   if ((right == left + 1) && array[left] >= array[right])
      return array[left];
   if ((right == left + 1) && array[left] < array[right])
      return array[right];
   int mid = (left + right)/2;
   if ( array[mid] > array[mid + 1] && array[mid] > array[mid - 1])
      return array[mid];
   if (array[mid] > array[mid + 1] && array[mid] < array[mid - 1])
      return getMaxElement(array, left, mid-1);
   else
      return getMaxElement(array, mid + 1, right);
}
int main() {
   int array[] = {8, 10, 20, 80, 100, 250, 450, 100, 3, 2, 1};
   int n = sizeof(array)/sizeof(array[0]);
   cout << "The maximum element is: " << getMaxElement(array, 0, n-1);
}