Spritekit - Spawn waves of monsters - sprite-kit

Question

I'm making a simple racing game in which the monsters are spawned (randomly) from 3 out of the 5 lanes in the portrait mode.
-(void)addEnemy
{
SKSpriteNode *Enemy;
Enemy = [SKSpriteNode spriteNodeWithImageNamed:#"Enemy1"];
[Enemy setScale:.65];
Enemy.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:Enemy.size];
Enemy.physicsBody.categoryBitMask = obstacleCategory;
Enemy.physicsBody.dynamic = YES;
Enemy.zPosition = 2;
Enemy.physicsBody.contactTestBitMask = TurtleCategory;
Enemy.physicsBody.collisionBitMask = 0;
Enemy.physicsBody.usesPreciseCollisionDetection = YES;
Enemy.name = #"Enemy";
//selecting random y position for Enemy
int r = (arc4random() % 5) ;
Enemy.position = CGPointMake(48+r*56,self.frame.size.height);
[self addChild:Enemy];
SKAction *actionMove =
[SKAction moveTo:CGPointMake(Enemy.position.x,-80)
duration:1.43];
[Enemy runAction:actionMove];
SKSpriteNode *Enemy2;
Enemy2 = [SKSpriteNode spriteNodeWithImageNamed:#"Enemy1"];
[Enemy2 setScale:.65];
//Adding SpriteKit physicsBody for collision detection
Enemy2.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:Enemy.size];
Enemy2.physicsBody.categoryBitMask = obstacleCategory;
Enemy2.physicsBody.dynamic = YES;
Enemy2.zPosition = 2;
Enemy2.physicsBody.contactTestBitMask = TurtleCategory;
Enemy2.physicsBody.collisionBitMask = 0;
Enemy2.physicsBody.usesPreciseCollisionDetection = YES;
Enemy2.name = #"Enemy2";
//selecting random y position for Enemy
int r2 = (arc4random() % 5) ;
Enemy2.position = CGPointMake(48+r2*56,self.frame.size.height);
[self addChild:Enemy2];
SKAction *actionMove2 =
[SKAction moveTo:CGPointMake(Enemy2.position.x,-80)
duration:1.43];
[Enemy2 runAction:actionMove2];
SKSpriteNode *Enemy1;
Enemy1 = [SKSpriteNode spriteNodeWithImageNamed:#"boss1"];
[Enemy1 setScale:.65];
//Adding SpriteKit physicsBody for collision detection
Enemy1.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:Enemy1.size];
Enemy1.physicsBody.categoryBitMask = obstacleCategory;
Enemy1.physicsBody.dynamic = YES;
Enemy1.zPosition =2;
Enemy1.physicsBody.contactTestBitMask = TurtleCategory;
Enemy1.physicsBody.collisionBitMask = 0;
Enemy1.physicsBody.usesPreciseCollisionDetection = YES;
Enemy1.name = #"Enemy1";
int r1 = (arc4random() % 5) ;
Enemy1.position = CGPointMake(48+r1*56,self.frame.size.height);
[self addChild:Enemy1];
SKAction *actionMove1 =
[SKAction moveTo:CGPointMake(Enemy1.position.x,-80)
duration:1.43];
[Enemy1 runAction:actionMove1];
However, one of problem of this code is that monsters are sometimes spawned on top of each other. Is there a better way to do this?
Thanks

Answer 1

- (CGFloat)randomValueBetween:(CGFloat)low andValue:(CGFloat)high {
return (((CGFloat) arc4random() / 0xFFFFFFFFu) * (high - low)) + low;
}
I found this piece of code from a raywenderlich tutorial I think.
What u can do is call,
CGFloat r1 = [self randomValueBetween:0 andValue:3];
CGFloat r2 = [self randomValueBetween:3 andValue:6]; etc
that might give you different values that u can use as offset.