Kata

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn't mttaer in waht oredr the ltteers in a wrod are, the olny iprmoetnt tihng is taht the frist and lsat ltteer be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

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Task:

Write a function which mix inner characters in each word,first and last character stays untouched.Notice that punctuation mark is not a part of a word!By word we define only alphanumeric characters.

Requirements:

-at least 10% of all changeable words must differ from original.

If you solve this kata,check how many percent of changeable words you have changed.If you reach 100% you will get a reward!