Peak element

An element is called a peak element if its value is not smaller than the value of its adjacent elements(if they exists).

Given an array arr[] of size N, find the index of any one of its peak elements.

Note: The generated output will always be 1 if the index that you return is correct. Otherwise output will be 0.

• Time : O(logn)
• Space : O(1)

c++

class Solution
{
public:
    int peakElement(int arr[], int n) {
        if(n == 1) return 0;
        if(n == 2) {
            if(arr[0] == arr[1]) return -1;
            return arr[0] > arr[1] ? 0 : 1;
        }
        int l = 0, r = n - 1;
        while(l <= r) {
            int m = l + (r - l) / 2;

            if(m == 0) {
                if(arr[m + 1] < arr[m]) return m;
                return -1;
            } else if(m == n - 1) {
                if(arr[m - 1] < arr[m]) return m;
                return -1;
            } else {
                if(arr[m] > arr[m - 1] and arr[m] > arr[m + 1]) return m;
                if(arr[m + 1] > arr[m - 1]) l = m + 1;
                else r = m - 1;
            }
        }
        return -1;
    }
};