Binary Search Tree Iterator

class BSTIterator:
    # @param root, a binary search tree's root node
    def __init__(self, root):
        self.stack = []
        self.pushLeft(root)

    # @return a boolean, whether we have a next smallest number
    def hasNext(self):
        return self.stack

    # @return an integer, the next smallest number
    def next(self):
        top = self.stack.pop()
        self.pushLeft(top.right)
        return top.val
    
    def pushLeft(self, node):
        while node:
            self.stack.append(node)
            node = node.left

class BSTIterator {
public:
    BSTIterator(TreeNode *root) {
        while (root) {
            s.push(root);
            root = root->left;
        }
    }

    /** @return whether we have a next smallest number */
    bool hasNext() {
        return !s.empty();
    }

    /** @return the next smallest number */
    int next() {
        TreeNode *n = s.top();
        s.pop();
        int res = n->val;
        if (n->right) {
            n = n->right;
            while (n) {
                s.push(n);
                n = n->left;
            }
        }
        return res;
    }
private:
    stack<TreeNode*> s;
};

public class BSTIterator {
    private Stack<TreeNode> stack = new Stack<TreeNode>();
    
    public BSTIterator(TreeNode root) {
        pushAll(root);
    }

    /** @return whether we have a next smallest number */
    public boolean hasNext() {
        return !stack.isEmpty();
    }

    /** @return the next smallest number */
    public int next() {
        TreeNode tmpNode = stack.pop();
        pushAll(tmpNode.right);
        return tmpNode.val;
    }
    
    private void pushAll(TreeNode node) {
        for (; node != null; stack.push(node), node = node.left);
    }
}