小敏想用二分法对关键字14进行查找，请你帮她补全如下代码：

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！')