162. Find Peak Element

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

(1) Java

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

(2) Python

class Solution:
    def findPeakElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if not nums:
            return -1
        left, right = 0, len(nums)-1
        rst = 0
        while left <= right:
            mid = left + int((right-left)/2)
            if mid-1 >= 0:
                leftLow = nums[mid] > nums[mid-1]
            else:
                leftLow = True
            if mid+1 < len(nums):
                rightLow = nums[mid] > nums[mid+1]
            else:
                rightLow = True
            if leftLow and rightLow:
                return mid
            elif leftLow:
                left = mid+1
            else:
                right = mid-1
        return rst

(3) Scala