季更57/90

def binary_search(list,item):
    low = 0 //最小索引
    high = len(list) - 1 //最大索引
    while low <= high: //最小索不可能超过最大索引
        mid = int((low+high)/2) //取中间索引
        guess = list[mid] //设置当前索引值
        if guess == item: //当前值等于目标值
            return mid //返回当前索引
        if guess > item: //当前值大于目标值
            high = mid - 1 //降低最大索引
        if guess < item: //当前值小于目标值
            low = mid +1 //增大最小索引
    return None //找不到返回空

list = [1,2,3,4,5,6]
print(binary_search(list,3)) //2