title: Find the unique element in an unordered array consisting of duplicates
body: <p>For example, if L = [1,4,2,6,4,3,2,6,3], then we want 1 as the unique element. Here's pseudocode of what I had in mind:</p>
  
  <p>initialize a dictionary to store number of occurrences of each element: ~O(n), 
  look through the dictionary to find the element whose value is 1: ~O(n)</p>
  
  <p>This ensures that the total time complexity then stay to be O(n). Does this seem like the right idea?</p>
  
  <p>Also, if the array was sorted, say for example, how would the time complexity change? I'm thinking it would be some variation of binary search which would reduce it to O(log n). </p>