Given a tree and a sum, return true if there is a path from the root down to a leaf, such that adding up all the values along the path equals the given sum.

RootToLeafSum.java

public boolean isSumExists( Node root, int sum ){
  if( root == null && sum != 0 ){
    return false;
  }
  int currentNodeSum = sum - root.getData();
  if( currentNodeSum == 0 ){
    return true;
  } else{
    return ( isSumExists( root.getLeftChild(), currentNodeSum ) || isSumExists( root.getRightChild(), currentNodeSum ) );
  }
}