# 162. Find Peak Element

## 1. Question

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.

## 2. Examples

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.


## 3. Constraints

• 1 <= nums.length <= 1000
• -231 <= nums[i] <= 231 - 1
• nums[i] != nums[i + 1] for all valid i.

## 5. Solutions

nums[-1] = nums[n] = -∞

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