A58588. 小敏想用二分法对关键字14进行查找，请你帮她补全代码lst=[3,12,7,45,9,10,31,90,1,23,14,52]

小敏想用二分法对关键字14进行查找，请你帮她补全代码

lst=[3,12,7,45,9,10,31,90,1,23,14,52]
      ①      
key=14
n=len(a)
i,j=0,n-1
flag=-1
while       ②      :
    mid=(i+j)//2
    if key==a[mid]:
        flag=mid
        break
    elif key>a[mid]:
              ③      
    else:
        j=mid-1
if       ④      :
    print(str(key)+'没找到！')
else:
    print(str(key)+'已找到！')