find_peak.cpp

/*
https://leetcode.com/problems/find-peak-element/

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

Given an 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] = -∞.

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.
*/
class Solution {
public:
    int findPeakElement(vector<int>& nums) {
         int low = 0, high = nums.size() - 1;
        while (low < high - 1) {
            int mid = (low + high) / 2;
            if (nums[mid] > nums[mid - 1] && nums[mid] > nums[mid + 1]) 
                return mid;
            else if (nums[mid] > nums[mid + 1]) 
                    high = mid - 1;
                 else 
                    low = mid + 1;    
        }
        return nums[low] > nums[high] ? low : high;
        
    }
};