title: How to solve one of this CodingBat java method?
body: <p>Here is my homework:</p>
  
  <blockquote>
    <p>We'll say that 2 strings "match" if they are non-empty and their first chars are the same. Loop over and then return the given array of non-empty strings as follows: if a string matches an earlier string in the array, swap the 2 strings in the array. When a position in the array has been swapped, it no longer matches anything. Using a map, this can be solved making just one pass over the array. </p>
  
  <pre><code>allSwap(["ab", "ac"]) → ["ac", "ab"]
  
  allSwap(["ax", "bx", "cx", "cy", "by", "ay", "aaa", "azz"]) → ["ay", "by", "cy", "cx", "bx", "ax", "azz", "aaa"]
  
  allSwap(["ax", "bx", "ay", "by", "ai", "aj", "bx", "by"]) → ["ay", "by", "ax", "bx", "aj", "ai", "by", "bx"]
  </code></pre>
  </blockquote>