title: How to control the enemy in Tower Defense using Sprite Kit?
body: <p>I am new to IOS development. I want to make a Tower Defense game.</p>
  
  <p>So here are some problems I have:</p>
  
  <ol>
  <li><p>If I create a method to add enemies in an array, how do I know which enemy walking at the front? I want my towers always hit the front one.</p></li>
  <li><p>I want to create a AOE(area of effect) damage, how to detect all the enemies that standing on a certain area?</p></li>
  <li><p>Maybe like question 2, I want a ambient effect too, how to detect which enemy is near the enemy that got hit?</p></li>
  </ol>
  
  <p>All answers will be appreciated!Thanks!</p>