Given a word (or any sequence of letters) as input, you must interpolate between each letter such that each adjacent pair of letters in the result is also adjacent on a QWERTY keyboard, as if you typed the input by walking on a giant keyboard. For example, 'yes' might become 'ytres', 'cat' might become 'cxzawert'.

Rules:

• 
  

  This is the keyboard format you should use:

  
  
  

  qwertyuiop

 asdfghjkl

  zxcvbnm

  
  
  

  Any pair of keys which is touching in this layout is considered adjacent. For instance, 's' and 'e' are ajacent, but 's' and 'r' are not.

  
  


• The input "word" will consist of any sequence of letters. It will have only letters, so you don't have do deal with special characters.


• The input can be in any convenient form: stdin, a string, a list, etc. Letter case does not matter; you can take whatever is more convenient.


• The output can be in any convenient form: stdout, a string, a list, etc. Letter case does not matter, and it does not need to be consistent.


• Any path across the keyboard is valid, except that you cannot cross the previous letter again before getting to the next letter. For example, 'hi' could become 'hji' or 'hjnbgyui', but not 'hbhui'.


• A letter is not ajacent with itself, so 'poll' cannot become 'poll'. Instead it would need to become something like 'polkl'.


• No output letters are allowed before or after the word. For example, 'was' cannot become 'trewas' or 'wasdfg'.

This is code golf, the shortest answer in bytes wins.

Python 2, 83 bytes

lambda s:re.findall('.*?'.join(s),'qwertyuioplkmnjhbvgfcxdsza'*len(s))[0]

import re

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Walks the entire keyboard until the word is written.

JavaScript (ES6), 70 bytes

Same strategy as TFeld.

s=>'qazsxdcfvgbhnjmklpoiuytrew'.repeat(s.length).match(s.join`.*?`)[0]

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Japt -g, 24 bytes

;D·ÎÔ+D·Årí)pUl)fU¬q".*?

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Takes input in all caps. Very similar to the other answers otherwise.

Explanation:

;                           :Set D to the keyboard layout

 D·Î                        :Get the first row of keys

    Ô                       :Reversed

     +                      :Concat

      D·Å                   :The other two rows

         rí)                :Interleaved

            p               :Repeat that string

             Ul)            : A number of times equal to the length of the input

                f           :Get the substrings that match

                 U          : The input

                  ¬         : split into characters

                   q".*?    : and joined back with ".*?"

                            :Implicitly output just once of the matches