Day 7

[vaskoz]

Good morning! Here's your coding interview problem for today.

This problem was asked by Facebook.

Given the mapping a = 1, b = 2, ... z = 26, and an encoded message, count the number of ways it can be decoded.

For example, the message '111' would give 3, since it could be decoded as 'aaa', 'ka', and 'ak'.

You can assume that the messages are decodable. For example, '001' is not allowed.

[charliecys]

Hi Vaskoz!

I believe your solution will fail on "1111127".

It should expect 13 which consist of the following:
aaaaabg, aaakbg, aakabg, akaabg, kaaabg, kkabg, kakbg, akkbg, aaaalg, aaklg, akalg, kaalg, kklg

[vaskoz]

Hi @charlieysc !

I added your testcase to my "day 7" tests with this commit and the test appears to pass on your testcase with the code as-is.

Separately, I also rewrote my solution to make it easier to read. My previous solution processed the input from the back. My new solution processes the input from the front.

The simplification also resulted in a small speedup.
BEFORE:

go test -cover -race -bench=.                                              
goos: darwin
goarch: amd64
pkg: github.com/vaskoz/dailycodingproblem-go/day7
BenchmarkNumberOfDecodings-12    	  200000	     10726 ns/op
PASS
coverage: 100.0% of statements
ok  	github.com/vaskoz/dailycodingproblem-go/day7	3.280s

AFTER:

go test -cover -race -bench=.
goos: darwin
goarch: amd64
pkg: github.com/vaskoz/dailycodingproblem-go/day7
BenchmarkNumberOfDecodings-12    	  200000	      9388 ns/op
PASS
coverage: 100.0% of statements
ok  	github.com/vaskoz/dailycodingproblem-go/day7	3.000s

[charliecys]

Whoops! Mistake on my part. Yes, your solution works as-is.