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mediumDSA

How do you find a peak element in an array?

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01

Understand the problem

Explain peak finding in O(log n).

binary-searcharrays
02

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Nudge consolestandby

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03

Study the solution

A peak is greater than its neighbors. Use binary search: if nums[mid] < nums[mid+1], a peak must lie to the right, so go right; otherwise go left (including mid). This converges to a peak in O(log n) without scanning everything.

Solution ready — 2 min read

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04

Read the code

Binary search toward the peak
Run Playground
def find_peak(nums):
    lo, hi = 0, len(nums) - 1
    while lo < hi:
        mid = (lo + hi) // 2
        if nums[mid] < nums[mid + 1]:
            lo = mid + 1          # uphill to the right
        else:
            hi = mid              # peak is mid or to the left
    return lo


# --- demo ---
print(find_peak([1, 2, 3, 1]))   # 2  (nums[2] = 3 is a peak)
05

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