Decode Ways

Problem

Count the number of ways to decode a digit string s where 1 maps to A through 26 mapping to Z.

Use dynamic programming: a single digit can stand alone when it is not zero, and a two-digit group is valid only when it lies between 10 and 26. Return 0 for the empty string or any string that cannot be fully decoded.

Hint

A leading zero can only be consumed as the second digit of 10 or 20.

Test cases

case 1

in: ["12"]

expected: 2

case 2

in: ["226"]

expected: 3

case 3

in: ["06"]

expected: 0

case 4

in: ["10"]

expected: 1

case 5

in: ["27"]

expected: 1

case 6

in: [""]

expected: 0

Starter codePython

def num_decodings(s):
    # Your code here
    pass

6 test cases · run your code against them in the editor