findpeak.cpp

#include <iostream>
#include <vector>
using namespace std;
int findpeak(vector<int> &input)
{
    int n = input.size();
    int lo = 0, hi = n - 1;
    while (lo <= hi)
    {
        int mid = lo + (hi - lo) / 2;
        if (mid == 0)
        {
            if (input[mid] < input[mid + 1])
            {
                return 0;
            }
            else
            {
                return 1;
            }
        }
        else if (mid == n - 1)
        {
            if (input[mid] > input[mid - 1])
            {
                return n - 1;
            }
            return n - 2;
        }
    }
    else
    {
        if (input[mid] > input[mid + 1] and input[mid] > input[mid - 1])
        {
            return mid;
        }
        else if (input[mid] > input[mid - 1])
        {
            lo = mid + 1;
        }
        else
        {
            hi = mid - 1;
        }
    }
}