title: Is there any algorithm that can solve ANY traditional sudoku puzzles, WITHOUT guessing (or similar techniques)?
body: <p>Is there any algorithm that solves ANY traditional sudoku puzzle, WITHOUT guessing?</p>
  
  <p>Here Guessing means trying an candidate and see how far it goes, if a contradiction is found with the guess, backtracking to the guessing step and try another candidate; when all candidates are exhausted without success, backtracking to the previous guessing step (if there is one; otherwise the puzzle proofs invalid.), etc.</p>
  
  <p>EDIT1: Thank you for your replies. </p>
  
  <p>traditional sudoku means 81-box sudoku, without any other constraints. Let us say the we know the solution is unique, is there any algorithm that can GUARANTEE to solve it without backtracking? Backtracking is a universal tool, I have nothing wrong with it but, using a universal tool to solve sudoku decreases the value and fun in deciphering (manually, or by computer) sudoku puzzles. </p>
  
  <p>How can a human being solve the so called "the hardest sudoku in the world", does he need to guess?</p>
  
  <p>I heard some researcher accidentally found that their algorithm for some data analysis can solve all sudoku. Is that true, do they have to guess too?</p>