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173.cpp
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// usingStack.cpp
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
stack<TreeNode *> st;
public:
BSTIterator(TreeNode *root) {
while (root != NULL) {
st.push(root);
root = root->left;
}
}
/** @return whether we have a next smallest number */
bool hasNext() { return !st.empty(); }
/** @return the next smallest number */
int next() {
TreeNode *p = st.top();
st.pop();
int value = p->val;
p = p->right;
while (p != NULL) {
st.push(p);
p = p->left;
}
return value;
}
};
/**
* Your BSTIterator will be called like this:
* BSTIterator i = BSTIterator(root);
* while (i.hasNext()) cout << i.next();
*/