I'm generating some random x and y coordinates for a player in a game:
var xcoordRed = Math.floor((Math.random() * 790) +1); var ycoordRed = Math.floor((Math.random() * 400) +1); But I need to exclude from xcoordRed the range 325 - 375 and from ycoordRed 150 - 250.
How would I go about doing this efficiently?
Simple math, reduce the range of the random call by the difference of the excluded range, and then if the random value is bigger than the lower exclusion delimiter, just increase it by the exclusion difference. Meaning:
var diff = 375 - 325; // add 1 if inclusive var xcoordRed = Math.floor((Math.random() * (790 - diff)) +1); if (xcoordRed >= 325) xcoordRed += diff; // the same approach goes for Y This means that, if the random value is, say, 324, it will remain 324. But, if it's 330, it will become 380, etc. The highest possible random number, 740, will become 790, of course.
var r = document.getElementById('r'); function gen() { var diffx = 375 - 325; var diffy = 250 - 150; var xcoordRed = Math.floor((Math.random() * (790 - diffx)) + 1); if (xcoordRed >= 325) xcoordRed += diffx; var ycoordRed = Math.floor((Math.random() * (400 - diffy)) + 1); if (ycoordRed >= 150) ycoordRed += diffy; r.textContent = 'X: ' + xcoordRed + ' Y: ' + ycoordRed; }<button onclick="gen()">Generate</button> <div id="r"></div>You can create an array of allowed list and get a random value from allowed range. Not sure if this is very efficient, but it can work with multiple chunks to be excluded.
function getArrayWithExcludes(min, max, exclude) { var _tmp = []; for (var i = min; i < max; i++) { if (!exclude.some(function(item) { return i > item.min && i < item.max })) _tmp.push(i); } return _tmp; } function getRandomValue(arr) { var len = arr.length; var random = Math.floor(Math.random() * len) % len; return arr[random]; } var xExRange = [{ min: 10, max: 50 }, { min: 325, max: 375 }]; var yExRange = [{ min: 150, max: 250 }]; var xRange = getArrayWithExcludes(0, 790, xExRange); var yRange = getArrayWithExcludes(0, 400, yExRange); var xcoordRed = getRandomValue(xRange); var ycoordRed = getRandomValue(yRange); document.write("<pre>" + JSON.stringify({x:xcoordRed,y: ycoordRed},0,4) + "</pre>");