Find Peak Element

Problem

A peak element is an element that is strictly greater than its neighbors. Given a 0-indexed 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.

Examples

The brute-force approach

Scan left to right. Return the first index where the element is greater than both neighbors.

for i in range(n):
    left_ok = (i == 0 or nums[i] > nums[i-1])
    right_ok = (i == n-1 or nums[i] > nums[i+1])
    if left_ok and right_ok:
        return i

O(n) — linear scan.

Spotting the pattern

This is a Binary Search problem. The key question to ask yourself:

If nums[mid] < nums[mid+1], why is it guaranteed that a peak exists somewhere in nums[mid+1..right]?

Answering that is where it clicks, and it's exactly what the guided walkthrough below builds with you: the pattern reasoning, a progressive hint ladder that never spoils the answer, a row-by-row dry run, the optimized solution, and an in-browser editor to run your code against real test cases.