Complete the algorithm for generating Sudoku puzzles

Question

I have a code below but there's a problem with the current implementation in the function entriesToDel. It will not always produce n distinct co-ordinates to be turned blank in a puzzle. It should always produce an array with n elements consisting of two-element arrays storing the co-ordinates of an element and every element of the output should produce distinct co-ordinates but I'm not sure how to do that as I'm quite new to this.

// a function to randomly select n (row,column) entries of a 2d array
function entriesToDel(n) {
        var array = [];
        for (var i = 0; i < n; i++) {
            var row = Math.round(3*Math.random());
            var col = Math.round(3*Math.random());
            array.push([row,col]);
        }
        return array;
}

Create an array with all possible coordinates. [Shuffle it](https://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array). Take the first n elements. — James, Mar 07 '22 at 18:04

dtpnftscdsatp · Answer 1 · 2022-03-07T18:24:32.517

A simple solution would be using a set instead of an array and add random numbers until you have enough unique entries.

In case you dont know what a set is: A set works similarly to an array, but it does not allow for duplicates (duplicates will be ignored). (It also does not give elements a fixed position; you can't access an entry of a set with set[i])

const size = 3 // define size of grid in variable

function entriesToDel(n) {

 // create set of positions
 const positions = new Set() // create set
 while(positions.size < n) { // repeat until set has enough entries
  positions.add(Math.floor((size ** 2) * Math.random())) // add random position (duplicates will be ignored by the set)
 }

 // convert set of positions to array of coordinates
 const cords = []
 for(const position of positions) { // iterate through positions
  // convert position to column and row and add to array
  const row = Math.floor(position / size)
  const column = position % size
  cords.push([row, column])
 }

 return cords

}

This solution is nice and simple. An issue is that if you're really unlucky, the random number generator will keep on generating the same number, resulting in a possibly very long calculation time. If you want to exclude this (very unlikely) possibility, it would be reasonably to use the more complex solution provided by James.

Complete the algorithm for generating Sudoku puzzles

1 Answers1