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def binary_search(arr, target):
    # O(log n) · Ask AI Tutor ✦
    l, r = 0, len(arr) - 1
    while l <= r:
        mid = l + (r - l) // 2
        if arr[mid] == target: return mid
        elif arr[mid] < target: l = mid + 1
        else: r = mid - 1
    return -1