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| -rw-r--r-- | challenge-209/james-smith/README.md | 17 |
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diff --git a/challenge-209/james-smith/README.md b/challenge-209/james-smith/README.md index b190031e1c..908f8c30b2 100644 --- a/challenge-209/james-smith/README.md +++ b/challenge-209/james-smith/README.md @@ -30,6 +30,23 @@ sub special_bit_chars { scalar @_ } ``` +## Solution 2 + +As well as tracking from the front we can track from the back. + +First we need to note: + + * Last character must be a `0` + * If there is string ending in a `0` then we can ignore anything up to this, as `0` is always at the right hand character in a string; + * Additionally if the last two characters are 0 then we know that the answer is true. + * So breaking this down we need to work out whether the value is true or false if the list ends: `.....,1,0`. If the string consists of series of `n` pairs of `1`s then this converts to "...CCA" and so the last character is `A` so we return 0; If it is an odd number of 1s we have the string "...CCB" so the return value is false. + +```perl +sub special_bit_chars_reverse { + my$f,pop?return-1:pop||return 1; + $f=!$f,pop||last while@_; + ~~$f +} # Task 2: Merge Account |