二分查找

def cc(list1,value):
    if value in list1:
        beg = 0
        end = len(list1)
        count = 1
        while beg <= end:
            medain = int((beg+end)/ 2)       #例如：第4和第5個下座標的中間值等於4+5除以2，所以下面要用座標中間值-1 +1
            if l1[medain] == value:
                print(f"找到了{value},共找了{count}次")
                break
            elif l1[medain] > value:
                count += 1
                end = medain -1
            else:
                count += 1
                beg = medain + 1

    else:
        print(f"{value}不在列表裏面")
l1 = [1,2,3,4,5,6,7,8]
cc(l1,8)
# 法二：
def binary_search(sorted_array, val):
    if not sorted_array:
        return -1

    beg = 0
    end = len(sorted_array) - 1

    while beg <= end:
        mid = int((beg + end) / 2)
        if sorted_array[mid] == val:
            return mid
        elif sorted_array[mid] > val:
            end = mid - 1
        else:
            beg = mid + 1
    return -1


a = list(range(10))

# # 正常值
print(binary_search(a, 1))
print(binary_search(a, -1))
#
# # 邊界值
print(binary_search(a, 0))