title: hash table lookup time
body: <p>When we are insert/lookup an key in a hash table, textbook said it is O(1) time. Yet, how is possible to have an O(1) lookup time? If the hash table store the key in a vector, it will cost O(N), if in a binary tree, it will be O(logN). I just can't image some data structure with O(1) accessing time. </p>
  
  <p>Thanks!</p>