Interview Question


Country: United States




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/*
Not sure if there is a solution that will use no extra space strictly.
But, surely there is a trade off possible between speed and space.
For example you can scan 
  each row
  each column
  each sub-square
  
  and check if the values are in range and are NOT repeated.
  
  The validation step can be done using 9 units of extra memory
  for the standard size soduku board ( which is 9x9)
  
  In this type of check, each cell on the board will get
  subjected to a check 1+ times ( 3 times ?)
 */

- Makarand October 23, 2017 | Flag Reply
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Best I can think of is use a single 32-bits integer as "extra space". Use the last 9 bits and bit-wise operators to keep track of the numbers that are already in use as you check for row, column or 3x3 square. Don't forget to Initialize it to 0 before starting a new check!

- Anonymous October 24, 2017 | Flag Reply


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