def binary_search(nums: list[int], target: int) -> int:
    """Return index of target, or -1 if not found."""
    left, right = 0, len(nums) - 1

    while left < right:
        mid = (left + right) // 2
        if nums[mid] == target:
            return mid
        if nums[mid] < target:
            left = mid + 1
        else:
            right = mid - 1

    return -1