47. Find Peak Element

Topic :

binary search

Difficulty :

medium

Problem Link :

problem statement

A peak element is an element that is strictly greater than its neighbors.

Given a 0-indexed integer array nums, find a peak element, and return its index. If the array contains multiple peaks, return the index to any of the peaks.

You may imagine that nums[-1] = nums[n] = -∞. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.

You must write an algorithm that runs in O(log n) time.

Example 1:

Input: nums = [1,2,3,1]
Output: 2
Explanation: 3 is a peak element and your function should 
return the index number 2.

Example 2:

Input: nums = [1,2,1,3,5,6,4]
Output: 5
Explanation: Your function can return either index number 1 
where the peak element is 2, or index number 5 where
the peak element is 6.

Constraints:

1 <= nums.length <= 1000
-231 <= nums[i] <= 231 - 1
nums[i] != nums[i + 1] for all valid i.

solution

import java.io.*;
import java.util.*;
class PeakElement
{
   public static void main(String args[])
   {
       int nums[] = {1,2,3,1};
       System.out.println("peak element is found at index "+ findPeakElement(nums));
    }
   static int findPeakElement(int[] nums) {
      int low=0;
      int high=nums.length-1;
      
      while(low<high)
      {
        int mid=low+(high-low)/2;
         if(nums[mid]>nums[mid+1]) // peak is in the left half
             high=mid;
          else // peak is in the right half 
              low=mid+1;
      }
        return low;
    }
}