Leetcode162-Find Peek Element

Description

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] = -∞.

Example

Example 1:

1
2
3

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:

1
2
3

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

Time Complexity: $O(log^N)$
Space Complexity: $O(1)$

public int findPeakElement(int[] nums) {
    int left = 0;
    int right = nums.length - 1;
    while(left < right){
        int mid1 = (left + right)/2;
        int mid2 = mid1 + 1;
        if (nums[mid1] < nums[mid2])
            left = mid2;
        else
            right = mid1;
    }
    return left;
}