BST Iterator

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
stack<TreeNode *>st;
BSTIterator::BSTIterator(TreeNode *root) {
    while(!st.empty())
    st.pop();
    while(root)
    {   
        st.push(root);
        root=root->left;
    }
 
}

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

/** @return the next smallest number */
int BSTIterator::next() {
    TreeNode *curr; 
    int temp;
    curr=st.top()->right;
    temp=st.top()->val;
    st.pop();
    while(curr)
    {
        st.push(curr);
        curr=curr->left;
    }
    return temp;
    
}

/**
 * Your BSTIterator will be called like this:
 * BSTIterator i = BSTIterator(root);
 * while (i.hasNext()) cout << i.next();
 */