CareerCup

Use post-order traversal on the expression tree to evaluate that.
N-ary operator should not be a problem if we follow a correct post-order traversal.

This can be easily extended to N-ary trees, replace line10 with a loop that goes through all children and of course, push and pop all N operands.

do
{
	while( p != NULL )
		stack.push(p);
		p = p->left;
	while( !stack.empty() )
		last = stack.pop();
		lastbutone = stack.pop()
		if( isoperator(lastbutone)
			if( isoperand(lastbutone->right) ) - // line 10
				stack.push(operate(last, lastbutone, lastbutone->right));
			else{
				push(lastbutone);
				push(last);
				break;
		else
			stack.push(operate(last, stack.pop(), lastbutone));
}while( !stack.empty() );

call through inorder recursion and return (root->left root->value root->right)