1. Your comments arn't really helpful, and so I'd remove them. This is as the function names say all that you would want to know.
2. Using the inverse of 'split the line, change the sign', more commonly know as expanding not, you can change isInternal to be much simpler. Rather than using \$\overline{A} \lor \overline{B}\$ your can use \$\overline{A \land B}\$.
3. Since isInternal is the inverse of isLeaf you can just check that isLeaf(n.left) is not the same as isLeaf(n.right), as if it's not then there is one leaf and one internal.

And so you can change isWantedNode and isLeaf to:

private static boolean isWantedNode(TreeNode n) { if (n.left == null || n.right == null) return false; return isLeaf(n.left) != isLeaf(n.right); } private static boolean isLeaf(TreeNode n) { return n.left == null && n.right == null; } 

You may also want to change your return statment in strangeCount from a turnery, to addition of result and a turnery. And so I'd use:

private static int strangeCount(TreeNode h) { if (h == null) { return 0; } return strangeCount(h.left) + strangeCount(h.right) + (isWantedNode(h)?1:0); } 

1. Your comments arn't really helpful, and so I'd remove them. This is as the function names say all that you would want to know.
2. Using the inverse of 'split the line, change the sign', more commonly know as DeMorgan's laws, you can change isInternal to be much simpler. Rather than using \$\overline{A} \lor \overline{B}\$ your can use \$\overline{A \land B}\$.
3. Since isInternal is the inverse of isLeaf you can just check that isLeaf(n.left) is not the same as isLeaf(n.right), as if it's not then there is one leaf and one internal.

And so you can change isWantedNode and isLeaf to:

private static boolean isWantedNode(TreeNode n) { if (n.left == null || n.right == null) return false; return isLeaf(n.left) != isLeaf(n.right); } private static boolean isLeaf(TreeNode n) { return n.left == null && n.right == null; } 

You may also want to change your return statment in strangeCount from a turnery, to addition of result and a turnery. And so I'd use:

private static int strangeCount(TreeNode h) { if (h == null) { return 0; } return strangeCount(h.left) + strangeCount(h.right) + (isWantedNode(h)?1:0); }