Removing Sprite on collision and keeping copies of same sprite

Question

I have created a clone of the app Flappy Bird, and I’ve tried to add coins which appear randomly around the game. My problem is I try to make the coins disappear when the bird collides with them, but it has proven a difficult task. I have a function that spawns in a coin every 3 seconds; at first all the coins had the same categoryBitMask's, but then I changed it so every 3 coins had the the categoryBitMask of 1, 2, 3, recurring.

I have tried many slight variations on the code to get rid of the coins as they collide with the bird, sometimes the coins will disappear, but with other problems, like the wrong coins disappearing or no more coins spawning. Here is all the code I think you need to see for my problem:

class GameScene: SKScene, SKPhysicsContactDelegate {


    var bird = SKSpriteNode()
    var coin = SKSpriteNode()

    let birdGroup: UInt32 = 1
    let objectGroup: UInt32 = 2
    let gapGroup: UInt32 = 0 << 3
    let gapGroup2: UInt32 = 0 << 4
    let gapGroup3: UInt32 = 0 << 5

    var gameOver = 0

    var movingObjects = SKNode()

    var coinGroup1 = SKNode()
    var coinGroup2 = SKNode()
    var coinGroup3 = SKNode()



   override func didMoveToView(view: SKView) {



/********| Bird physics body |********/

        bird.physicsBody?.categoryBitMask = birdGroup
        bird.physicsBody?.collisionBitMask = gapGroup
        bird.physicsBody?.collisionBitMask = gapGroup2
        bird.physicsBody?.collisionBitMask = gapGroup3
        bird.physicsBody?.collisionBitMask = objectGroup
        bird.physicsBody?.contactTestBitMask = objectGroup

        bird.zPosition = 10

        self.addChild(bird)

/********| Bird physics body |********/



/********| Spawning coins |********/

  var timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: Selector("spawnPipes"), userInfo: nil, repeats: true)

}
 func spawnPipes(){


        var coinTexture = SKTexture(imageNamed: "coin.png")
        coin = SKSpriteNode(texture: coinTexture)
        coin.size.height = bird.size.height
        coin.size.width = bird.size.width
        coin.position = CGPoint(x: CGRectGetMidX(self.frame) + self.frame.size.width * 1.33, y: CGRectGetMidY(self.frame) + movementAmount2)
        coin.physicsBody = SKPhysicsBody(circleOfRadius: coin.size.height / 2)
        coin.physicsBody?.dynamic = false
        coin.runAction(moveAndRemove)


        coin.physicsBody?.contactTestBitMask = birdGroup


            if(i == 1){
                coin.physicsBody?.categoryBitMask = gapGroup
                coin.physicsBody?.collisionBitMask = gapGroup
                coinGroup1.addChild(coin)

            }else if(i == 2){
                coin.physicsBody?.categoryBitMask = gapGroup2
                coin.physicsBody?.collisionBitMask = gapGroup2
                coinGroup2.addChild(coin)

            }else if(i == 3){
                coin.physicsBody?.categoryBitMask = gapGroup3
                coin.physicsBody?.collisionBitMask = gapGroup3
                coinGroup3.addChild(coin)

            }else{
                i = 1


        }

    }

/********| Spawning coins |********/



/********| Removing coins |********/

func didBeginContact(contact: SKPhysicsContact) {

        if(gameOver == 0){
            if((contact.bodyA.categoryBitMask == gapGroup || contact.bodyB.categoryBitMask == gapGroup) || (contact.bodyA.categoryBitMask == gapGroup2 || contact.bodyB.categoryBitMask == gapGroup2) || (contact.bodyA.categoryBitMask == gapGroup3 || contact.bodyB.categoryBitMask == gapGroup3)){

            score++

            scoreLabel.text = "\(score)"
                if(contact.bodyA.categoryBitMask == gapGroup || contact.bodyB.categoryBitMask == gapGroup){
                    coinGroup1.removeAllChildren()
                }else if(contact.bodyA.categoryBitMask == gapGroup2 || contact.bodyB.categoryBitMask == gapGroup2){
                    coinGroup2.removeAllChildren()
                }else if(contact.bodyA.categoryBitMask == gapGroup3 || contact.bodyB.categoryBitMask == gapGroup3){
                    coinGroup3.removeAllChildren()
                }


/********| Removing coins |********/

Here is all of my code if this ^^^ isn't enough:

http://pastebin.com/7yGh5gBn