ericnormand

License plates

When you cross the border in a car, you have to abide by the local license plate regulations. (This is not true, but let's play pretend!) The order of the numbers and letters stays the same. But the groupings change from country to country.

Write a function that takes a license plate code (letters, digits, and hyphens in a string) and a group size (integer). The function should return a new string with the characters regrouped with hyphens between groups. All groups should be of the given size, except for perhaps the first, if there aren't enough characters to fill the group.

Examples

(regroup "A5-GG-B88" 3) ;=> "A-5GG-B88"

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Reverse words

Write a function that takes a string containing words (one or more sentences) and returns a string containing the words in reverse order.

Examples

(reverse-words "my name is Eric.") ;;=> "Eric. is my name"
(reverse-words "hello") ;;=> "hello"
(reverse-words "I love you") ;;=> "you love I"

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Lazy Fibonacci Sequence

Ah, the ubiquitous example of recursive functions. Well, this is not your traditional fibonacci sequence exercise.

We all know that the fibonacci sequence is defined as:

(fib 0) ;=> 1
(fib 1) ;=> 1
(fib n) ;=> (+ (fib (dec n)) (fib (dec (dec n))))

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Maxie and Minnie

The maxxie of a number n is the largest number you can achieve by swapping two of its digits (in decimal) (or choosing not to swap if it is already the largest possible). The minnie is the smallest with one swap (though you can't swap a zero digit into the most significant position).

Your task is to write a function that takes an integer and returns a tuple of the maxxie and minnie.

Examples

(swapmaxmin 213) ;=> [312, 123]

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Unfriendly neighors

Let's say we have a sequence of integers:

[1 3 2 4 1]

There are 4 spots between numbers where we could insert a new number (represented by commas):

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Custom sort order

The sort function sorts a collection based on its "natural ordering." sort-by allows you to sort a collection based on the natural ordering of the result of some function applied to the elements. Your task is to write a function sort-with which takes a sequence of elements that define the sort order.

Example

           ; define ordering               ; collection to sort
(sort-with [:breakfast :lunch :dinner]     #{:lunch :breakfast :dinner}) ;=> (:breakfast :lunch :dinner)
(sort-with [2 3 4 :jack :queen :king :ace] [4 2 4 :king 2]) ;=> [2 2 4 4 :king]

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Single letter swaps

Write a function that takes a sequence of strings and a target string. For each string in the sequence, determine if it is equal to the target string after exactly one letter swap. Return the sequence of letter pairs that are swapped, or nil if it doesn't exist.

Example

(letter-swaps ["bacd" "abdc" "abcde" "abcc" "abcd"] "abcd")
  ;=> [#{\a \b} #{\c \d} nil nil nil]

ericnormand

Word search

I'm fond of search that is forgiving of small mistakes. If you type a few letters from the word, even if you miss a letter, you should get the word.

Here's a simple, forgiving search function.

Write a function that takes two strings, a needle and a haystack. The function should return true if the needle is found in the haystack, with a few forgiving features:

• If the needle is fully contained in the haystack, it should return true.
• If the needle would be fully contained in the haystack, but for one or more missing letters, it should return true.

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Odd One Out

Write a function that takes a list of words (Strings). The function should return true if exactly 1 word differs in length from the others. It should return false in all other cases.

Examples

(odd-one? ["a" "b" "c"]) ;=> false
(odd-one? ["a" "b" "cc"]) ;=> true
(odd-one? ["abc" "aa" "xyz" "jj"]) ;=> false

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Primes in a number

Another contrived math problem. This one I think is actually pretty hard. It's got detecting primes, string manipulation, and combinations.

Your task is to write a function that takes an integer and finds all primes that are substrings of the decimal digits of that integer.

Examples

(find-primes 2) ;=> [2]