title: Check if Sudoku solution is valid
body: <p>You're given a solution to a Sudoku puzzle. Write the code to check if it's a valid solution.</p>
  
  <p>Your function signature should be:<br>
  <strong>boolean isValid(int starti, int startj, int endi, int endj)</strong></p>
  
  <p>Rules for those unfamiliar with Sudoku:</p>
  
  <ul>
  <li>Grid size is 9x9, divided into 9 regions of 3x3</li>
  <li>Each row must contain all digits from 1-9</li>
  <li>Each column must contain all digits from 1-9</li>
  <li>Each 3x3 square must contain all digits from 1-9</li>
  </ul>
  
  <p>I wasn't asked this question, but saw it on <a href="http://23.latest.careercup.appspot.com/question?id=7737673" rel="noreferrer">several</a> <a href="http://java.dzone.com/blogs/felipera/2011/02/24/interviewing-google-part-1" rel="noreferrer">places</a>. Checking the last rule might be the interesting part</p>