162_Find Peak Element.cpp

/*

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

Given a 0-indexed 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] = -∞. In other words, an element is always considered to be strictly greater than a neighbor that is outside the array.

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.

*/

/* Solution */

// Binary Search Approach
// Time Complexity:- O(logN)
// Space Complexity:- O(1)

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