Array Sorting Binary Search Two Pointers
Intermediate Level

Implement the findPeakUsingBinarySearch method that returns a peak element index using binary search.

The input contains an integer array nums and its length size. Your task is to return the index of a peak element.

A peak element is greater than its adjacent elements. For boundary positions, only the existing neighbour is considered.

For example, in [1,2,3,1], the value 3 at index 2 is a peak because it is greater than both adjacent values.

Example 1
Input:
nums (int[]) = [1,2,3,1]
size (int) = 4
Return:
(int) 2
Example 2
Input:
nums (int[]) = [1,2,1,3,5,6,4]
size (int) = 7
Return:
(int) 5
Example 3
Input:
nums (int[]) = [1]
size (int) = 1
Return:
(int) 0

Use binary search by comparing the middle value with its right neighbour.

If nums[mid] is less than nums[mid + 1], the array is rising at that point, so a peak must exist on the right side. Otherwise, a peak exists at mid or on the left side.

Continue until the search range becomes a single index. That index is a peak position.

Pseudocode:

function findPeakUsingBinarySearch(nums, size):
    left = 0
    right = size - 1
    while left < right:
        mid = left + (right - left) / 2
        if nums[mid] < nums[mid + 1]:
            left = mid + 1
        else:
            right = mid
    return left
Run your code to see the result.