leetCode No162. Find Peak Element

# Question
A peak element is an element that is greater than its neighbors.

Given an input array nums, where nums[i] ≠ nums[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that nums[-1] = nums[n] = -∞.

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: 1 or 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.

Note:

Your solution should be in logarithmic complexity.

Solution

From:Solution
In this case, the reasoning behind this can be understood by taking the following three cases which cover every case into which any problem can be divided.

Case 1:

All the numbers appear in a descending order.

Case 2:

All the elements appear in ascending order.

Case 3:

The peak appears somewhere in the middle.

Code

Python

class Solution:
    def findPeakElement(self, nums: List[int]) -> int:
        for i in range(0, len(nums)-1):
            if nums[i]>nums[i+1]:
                return i;
        return len(nums)-1;

Java

class Solution {
    public int findPeakElement(int[] nums) {
        for (int i=0; i<nums.length-1;i++){
            if(nums[i] > nums[i+1])
                return i;
        }
        return nums.length-1;
    }
}

C++

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        for (int i=0;i<nums.size()-1;i++){
            if (nums[i] > nums[i+1]){
                return i;
            }
        }
        return nums.size()-1;
    }
};