Too Long; Didn't Read
<a href="https://hackernoon.com/tagged/sudoku" target="_blank">Sudoku</a> is a number-placement <a href="https://hackernoon.com/tagged/puzzle" target="_blank">puzzle</a> where the objective is to fill a square grid of size ‘n’ with numbers between 1 to ‘n’. The numbers must be placed so that each column, each row, and each of the sub-grids (if any) contains all of the numbers from 1 to ‘n’.