Spritekit Add nodes without overlapping - swift

Question

I am trying to add 20 nodes at random locations on the screen without any of the nodes overlapping. Ive got the adding of the nodes at random locations part but I sill get some that overlap. What I have done so far is: I would be greatful for a point in the right dirrection.
while i < 20 {
let bubbleSize = self.frame.width / 12
let bubble = SKShapeNode(circleOfRadius: bubbleSize)
let widthL = -self.frame.size.width / 2 + bubble.frame.size.width / 2
let widthH = self.frame.size.width / 2 - bubble.frame.size.width / 2
let heightL = -self.frame.size.height / 2 + bubble.frame.size.height/ 2
let heightH = self.frame.size.height / 2 - bubble.frame.size.height / 2
var randWidth = randomNumber(range: widthL..<widthH)
var randHeight = randomNumber(range: heightL..<heightH)
bubble.fillColor = SKColor.cyan
bubble.position = CGPoint(x: randWidth, y: randHeight)
self.addChild(bubble)
}
func randomNumber(range: Range<CGFloat>) -> CGFloat {
//function that gives a random number of a range of CGFloats entered
let min = range.lowerBound
let max = range.upperBound
return CGFloat(arc4random_uniform(UInt32(CGFloat(max - min)))) + min
}

Answer 1

This should get you started. It essentially divides the screen into a grid and places the bubbles in grid locations while ensuring no other bubble is at that position. there is lots more you could do with this, like add slight random placement to the location (random generate some small offsets -2 to +2 for x and y values so that they don't look so perfectly placed).
let bubbleSize = self.frame.width / 12
let minX = 0 - self.frame.size.width / 2
let maxX = self.frame.size.width / 2
let minY = 0 - self.frame.size.height/ 2
let maxY = self.frame.size.height/ 2
var usedIndexes: [Int]!
let xRange = maxX * 2
let yRange = maxY * 2
let cols = xRange / bubbleSize
let rows = yRange / bubbleSize
func createBubbles(count: Int) {
for _ in 0..<count {
createBubble()
}
}
func createBubble() {
let index = findSlot()
let posX = index % cols
let posY = index / cols
let bubble = SKShapeNode(circleOfRadius: bubbleSize)
bubble.fillColor = SKColor.cyan
bubble.position = CGPoint(x: posX, y: posY)
self.addChild(bubble)
}
func findSlot() -> Int {
//preventative measure to stop endless loop from happening
guard usedIndexes.count > rows * cols else { return 0 }
let randomX = randomNumber(range: 0..<cols)
let randomY = randomNumber(range: 0..<rows)
let index = randomX + randomY * cols
if usedIndexes.contains(index) {
return findSlot()
}
else {
usedIndexes.append(index)
}
return index
}