Array Decision Making Binary Search
Intermediate Level

Implement the findPeakElementIndex method that returns an index of a peak element in the array.

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 neighbor values. The first element can be a peak if it is greater than the next value, and the last element can be a peak if it is greater than the previous value. For example, in [1,3,2], index 1 is the peak.

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

Check each position and compare it with its available neighbors.

For the first element, only compare it with the next element. For the last element, only compare it with the previous element. For middle elements, both left and right neighbors must be smaller.

Return the first index that satisfies the peak condition. If the array is empty, return -1.

Pseudocode:

function findPeakElementIndex(nums, size):
    if size == 0:
        return -1
    for i from 0 to size - 1:
        leftOk = i == 0 or nums[i] > nums[i - 1]
        rightOk = i == size - 1 or nums[i] > nums[i + 1]
        if leftOk and rightOk:
            return i
    return -1
Run your code to see the result.