How to write recursive and optimal solution for decoding the compressed string?

Question

I found a problem statement over the internet, was trying to solve it in ruby.

Input and output are self explanatory.

Eg. 1, Input : 2[abc]3[ab]c

Output : abcabcabcababababc

Explanation : 2 times abc and 3 times ab and then c

Eg. 2 Input : 2[3[a]b]

Output : aaabaaab

I tried this, But it doesn't work for multiple level.

num = 1
str = ""
"3[abc]4[ab]2[3[a]b]c".each_char do |ch|
  if ch.to_i != 0
    num = ch
  elsif ch == "["
    next
  elsif ch == "]"
    num.to_i.times { print str }
    str = ""
    num = 1
  else
    str << ch
  end
end

I was looking for recursive call.

"I was looking for recursive call" – you usually start with something that you can call like a method or proc. — Stefan
– Stefan, Commented Jan 6, 2021 at 18:04

Cary Swoveland · Accepted Answer · 2021-01-07 18:41:08Z

1

str = "2[abc]3[ab]c2[de]fg"

str.gsub(/(\d+)\[(\p{L}+)\]/) { $2*$1.to_i }  
  #=> "abcabcabababcdedefg"
  #    ^^^^^^
  #          ^^^^^^
  #                 ^^^^

We can write the regular expression in free-spacing mode to make it self-documenting.

/
(\d+)     # match one or more digits, save to capture group 1 
\[        # match '[' 
(\p{L}+)  # match one or more letters, save to capture group 2
\]        # match ']'
/x        # invoke free-spacing regex definition mode

For the first match,

$1 #=> "2"
$2 #=> "abc"

so the block becomes

"abc"*2
  #=> "abcabc"

answered Jan 7, 2021 at 18:41

Cary Swoveland

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