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;
}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.