title: how is sudoku np-complete?
body: <p>how is Sudoku an np-complete problem? according to wiki, to be classed as an np-complete problem it must satisfy 2 conditions</p>
  
  <ol>
  <li>problem must be in np</li>
  <li>every other problem in np must be reducible to given problem in polynomial time</li>
  </ol>
  
  <p>how is the second condition satisfied? can you give an example? for instance, I don't see any correlation between Sudoku problem and the travelling salesman problem or knapsack problem</p>
  
  <p>(kindly forgive poor formatting as I'm typing this question on my mobile device)</p>