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Find Peak Element

Finding any element greater than both neighbors in a 1D array, treating array edges as negative infinity.

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Given an array that isn’t guaranteed to be a single mountain, find any element greater than both its neighbors — edges count as -∞ neighbors, and any valid peak can be returned. (LeetCode 162)

def findPeakElement(arr):
    n = len(arr)


    if n == 1:
        return 0
    if arr[0] > arr[1]:
        return 0
    if arr[n-1] > arr[n-2]:
        return n-1


    low, high = 1, n - 2  # exclude edges, already checked
    while low <= high:
        mid = (low + high) // 2


        if arr[mid] > arr[mid-1] and arr[mid] > arr[mid+1]:
            return mid


        if arr[mid] < arr[mid+1]:  # climbing, peak is to the right
            low = mid + 1
        else:  # descending, peak is to the left
            high = mid - 1


    return -1  # failsafe, a peak always exists

Time: O(log n). Space: O(1). Think of it like walking a trail: climbing means the peak is ahead, descending means it’s behind, and at the top both sides go down.