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How does binary search work and what are its requirements?

Q: How does binary search work and what are its requirements?

**Intuition.** In a **sorted** array you never need to look at most elements. Check the middle: if it is too small the answer is to the right, too big it is to the left. Each step throws away **half** the remaining range — that is O(log n). target = 23, sorted array <rect x="126" y="40" width="52" height=

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binary-search

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Iterative binary search

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def binary_search(arr, target):
    lo, hi = 0, len(arr) - 1
    while lo <= hi:
        mid = lo + (hi - lo) // 2
        if arr[mid] == target:
            return mid
        if arr[mid] < target:
            lo = mid + 1
        else:
            hi = mid - 1
    return -1


# --- demo ---
print(binary_search([-1, 0, 3, 5, 9, 12], 9))   # 4
print(binary_search([-1, 0, 3, 5, 9, 12], 2))   # -1

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