Peak Index in a Mountain Array | Leetcode Solutions

 

An array arr a mountain if the following properties hold:

• arr.length >= 3
• There exists some i with 0 < i < arr.length - 1 such that:
  • arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
  • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Given a mountain array arr, return the index i such that arr[0] < arr[1] < ... < arr[i - 1] < arr[i] > arr[i + 1] > ... > arr[arr.length - 1].

You must solve it in O(log(arr.length)) time complexity.

 

Example 1:

Input: arr = [0,1,0]
Output: 1

Example 2:

Input: arr = [0,2,1,0]
Output: 1

Example 3:

Input: arr = [0,10,5,2]
Output: 1

 

Constraints:

• 3 <= arr.length <= 105
• 0 <= arr[i] <= 106
• arr is guaranteed to be a mountain array.

C++ Program Solution for Peak Index in a Mountain Array

class Solution {

public:

    int peakIndexInMountainArray(vector<int>& arr) {

       

        int s=0;

        int n=arr.size();

        int e=n-1;

        int mid= s+((e-s)/2);

        while(s<e)

        {

           if(arr[mid]<arr[mid+1])

           {

               s=mid+1;

               

           }

            else

            {

                e=mid;

               

            }

            mid=s+((e-s)/2);

        }

       

        return s;

    }

   

};

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