peak_element_in_mountain_array.cpp

// 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.

#include<iostream>
#include<vector>
using namespace std;

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;
    }
};