852. Peak Index in a Mountain Array

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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.

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class Solution {
public:
    int peakIndexInMountainArray(vector<int>& arr) {
       int s=0;
       int e=arr.size()-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; 
    }
};