Problem

Given a string of digits, determine how many ways it can be decoded into letters using the following mapping:

• "1" maps to 'A'
• "2" maps to 'B'
• ...
• "26" maps to 'Z'

Return the total number of valid decoding ways.

Examples

decodeMessage("1234")
// return 3
/* Why? "1234" can be decoded as:
"ABCD" (1 2 3 4)
"LCD" (12 3 4)
"AWD" (1 23 4) */