CareerCup

public static int getDisCnt(Tree root){
		Set<String> uniq = new HashSet<>();
		if(root == null){
			return 0;
		}
		return getMaxHelper(root, uniq);
	}
	
	private static int getMaxHelper(Tree root, Set<String> uniq){
		if(root == null){
			return uniq.size();
		}
		int l = 0;
		int r  = 0;
		if(uniq.add(root.data)){
			l = getMaxHelper(root.left, uniq);
			r = getMaxHelper(root.right, uniq);
			uniq.remove(uniq.size()-1);
		}
		else{
			l = getMaxHelper(root.left, uniq);
			r = getMaxHelper(root.right, uniq);
		}
		return Math.max(l, r);

}

int GetDistinctCnt(TreeNode )
{
     HashTable t = new HashTable();
     GetMax(n, t);
     return t.Count;
}

void GetMax(TreeNode n, HashTable t)
{
     if(n!= null) 
     {
	if(!t.ContainsKey(n.Value))
	{
	     t.Add(n.Value, n);
        }
	GetMax(n.Right, t);
        GetMax(n.Left, t);
     }
}

public static int maxDistinct(Tree root){
Set<String> uniq = new HashSet<>();
if(root == null){
return 0;
}
return getMax(root, uniq);
}

private static int getMax(Tree root, Set uniq){
if(root == null){
return uniq.size();
}
int l = 0;
int r = 0;
if(uniq.add(root.data)){
l = getMax(root.left, uniq);
r = getMax(root.right, uniq);
uniq.remove(uniq.size()-1);
}
return Math.max(l,r);
}

Use a hashset to keep track of unique nodes. While traversing the tree.

public static int getDisCnt(Tree root){
		Set<String> uniq = new HashSet<>();
		if(root == null){
			return 0;
		}
		return getMaxHelper(root, uniq);
	}
	
	private static int getMaxHelper(Tree root, Set<String> uniq){
		if(root == null){
			return uniq.size();
		}
		int l = 0;
		int r  = 0;
		if(uniq.add(root.data)){
			l = getMaxHelper(root.left, uniq);
			r = getMaxHelper(root.right, uniq);
			uniq.remove(uniq.size()-1);
		}
		else{
			l = getMaxHelper(root.left, uniq);
			r = getMaxHelper(root.right, uniq);
		}
		return Math.max(l, r);

}