PeakElement

package array;

/**
 * <b>IDeserve <br>
 * <a href="https://www.youtube.com/c/IDeserve">https://www.youtube.com/c/IDeserve</a>
 * <br><br>
 * Peak Element</b><br>
 * Given an array of size n, find a peak element. Peak element is the element which is greater or equal to all its neighbors.<br><br>
 * <br><br>
 * Ex. Array [1,4,3,6,7,5]
 * <br>
 * Output: 4
 * <br><br>
 * <a href="https://www.youtube.com/watch?v=zOyOwDEF1Rc">Peak Element - Youtube Link</a> 
 * @author Saurabh
 *
 */
public class PeakElement {

	public static Integer getPeakElement(int[] array) {
		
		if(array == null || array.length == 0) {
			return null;
		}
		
		int n = array.length;
		
		int start = 0;
		int end = n - 1;
		
		while(start <= end) {
			int mid = (start+end)/2;
			
			if((mid == 0 || array[mid-1] <= array[mid]) &&
				(mid == n-1 || array[mid] >= array[mid+1])) {
				return array[mid];	// array[mid] is peak element
			}
			else {
				if(mid>0 && array[mid-1] > array[mid]) {
					end = mid-1;
				} else {
					start = mid+1;
				}
			}
		}
		return null;
	}
	
	public static void main(String[] args) {
		{
			int[] array = { 15, 20, 25, 35, 45, 50, 60 };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = { 5,4,3,2,1 };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = { 1,4,3,6,7,5 };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = { 1,3,5,7,6,4,2 };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = { 1 };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = {  };
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
		{
			int[] array = null;
			Integer peak = getPeakElement(array);
			System.out.println(peak != null ? "Peak Element is " + peak : "No peak element!");
		}
	}

}