def numDecodings(A):

if len(A) == 0:

return 0

if int(A[0]) == 0:

return 0

n = len(A)

result = [0 for _ in range(0, n + 1)]

result[0] = result[1] = 1

for i in range(1, n):

v1 = int(A[i:i + 1])

v2 = int(A[i - 1:i + 1])

if 0 < v1 <= 9:

result[i + 1] = result[i]

if 10 <= v2 <= 26:

result[i + 1] = result[i + 1] + result[i - 1]

if result[i + 1] == 0:

return 0

answer = result[n]

return answer

print(numDecodings("1204"))