CareerCup

Given a binary tree and 2 values. Write a function to find the 1st common ancestor in the binary tree.

The method I have used is that the common ancestor is the one who would have value between the given 2 values. So for example if the values are 3 and 10. so the common ancestor would be a node with value greater than 3 and less than 10.

here is my code.

public Node getCommonAncestor(Node root,int a, int b)
{
     if((root.value>a && root.value<b) || (root.value<a&&root.value>b))
   {
     if(checkvalue(root,a) && checkvalue(root,b))
     {
         return root;
      }
     else
      {
        return null;
        }
   }
  else if(root.value>a && root.value>b)
   {
        if(root.left != null)
         {
             return getCommonAncestor(root.left,a,b)
         }
         else
         {
            return null;
           }
    }
   else
   {
   
        if(root.right != null)
         {
             return getCommonAncestor(root.right,a,b)
         }
         else
         {
            return null;
           }
    }
}
public boolean checkvalue(Node root,int a)
{
    if(check.value == a)
   {
     return true;
   }
   else if(check.value>a)
    {
       if(check.left != null)
      {
         return checkvalue(check.left,a)
       }
      else
      {
          return false;
       }
     }
     else
     {
          if(check.right != null)
      {
         return checkvalue(check.right,a)
       }
      else
      {
          return false;
       }
      }
}
class Node
{
    int value;
    Node left;
    Node right;
}

Can you suggest whether I am right or not?