Find Peak Element of an Array Using Binary Search in C++

In this C++ program, we find out one of the peaks in the array can be found Using binary search approach. This algorithm returns the first peak found as a result with time complexity of the algorithm is O(log(n)).

Algorithm

Begin
   PeakElement() function has ‘arr’ the array of data, start and end index in the argument list.
   Assign the mid of subpart of the array.
   If mid is at the boundary index and value at mid is higher than its neighbor then return mid as peak.
   If the value at mid is greater than both of its neighbors then return mid as peak.
   If the value at the right of mid is greater than mid then send second sub-part of the array into PeakElement() as argument.
   If the value at the left of mid is greater than mid then send first sub-part of the array into PeakElement() as argument.
End

Example Code

#include<iostream>
using namespace std;
int PeakElement(int a[], int start, int end) {
   int i, mid;
   mid = (end+start+1)/2;
   if((a[mid] > a[mid+1] && mid == start)||(a[mid] > a[mid-1] && mid == end)) {
      return a[mid];
   } else if(a[mid] < a[mid-1] && a[mid] > a[mid+1]) {
      return a[mid];
   } else if(a[mid] <= a[mid+1]) {
      return PeakElement(a, mid+1, end);
   } else if(a[mid] <= a[mid-1]) {
      return PeakElement(a, start,mid-1);
   }
}
int main() {
   int n, i, p;
   cout<<"\nEnter the number of data element: ";
   cin>>n;
   int arr[n];
   for(i = 0; i < n; i++) {
      cout<<"Enter element "<<i+1<<": ";
      cin>>arr[i];
   }
   p = PeakElement(arr, 0, n-1);
   cout<<"\nThe peak element of the given array is: "<<p;
   return 0;
}

Output

Enter the number of data element: 5
Enter element 1: 45
Enter element 2: 26
Enter element 3: 70
Enter element 4: 60
Enter element 5: 15
The peak element of the given array is: 70