Find the maximum element which is common in two arrays?

Question

Given two arrays, how to find the maximum element which is common to both the arrays?

I was thinking of sorting both the arrays(n log n) and then perform the binary sear

Answer 1

You can but using O(N) space.
Just go through the first array and place all elements in a HashTable. This is O(N)
Then go through the second array keeping track of the current maximum and checking if the element is in the HashTable. This is also O(N) . So total runtime is O(N) and O(N) extra space for the HashTable

Example in Java:

public static int getMaxCommon(int[] a, int[] b){  
  Set firstArray = new HashSet(Arrays.asList(a));  
  int currentMax = Integer.MIN_VALUE;  
  for(Integer n:b){  
     if(firstArray.contains(n)){  
         if(currentMax < n){  
              currentMax = n  
         }
     }   
  }   
  return currentMax;  
}