WEC Codebuddy week5 3rd sem solution

week5.cpp

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

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

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

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