91. Decode Ways

Description:

Solution:

We should consider if the number is two digits case: 10, 20

Since A-Z is 26, 20-26 is the right range for decode.

 

ex) s = "112"

dp[3] = 1

dp[2] = 1 

dp[1] = 1 + 1 = 2

dp[0] = 2 + 1 = 3

 

Space Complexity: O(1)