def binary_search(list: list, target: str):
    """binary search
    
    Args:
        list (list): sorted list
        target (str): search target
    """
    low = 0
    high = len(list) - 1
    while low <= high:
        mid = (low + high) // 2
        pick = list[mid]
        if pick == target:
            return mid
        if pick > target:
            high = mid -1
        else:
            low = mid + 1
    return None