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173-Binary-Search-Tree-Iterator.cpp
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173-Binary-Search-Tree-Iterator.cpp
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/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
public:
BSTIterator(TreeNode *root) {
cur_ = findMostLeft(root);
}
/** @return whether we have a next smallest number */
bool hasNext() {
return cur_ != NULL;
}
/** @return the next smallest number */
int next() {
if (cur_ == NULL) return 0;
int val = cur_->val;
if (cur_->right != NULL)
cur_ = findMostLeft(cur_->right);
else{
if (!stack_.empty()){
cur_ = stack_.top();
stack_.pop();
} else
cur_ = NULL;
}
return val;
}
TreeNode* findMostLeft(TreeNode* root){
if (root == NULL) return NULL;
while (root->left != NULL){
stack_.push(root);
root = root->left;
}
return root;
}
private:
stack<TreeNode*> stack_;
stack<bool> is_right_;
TreeNode* cur_;
};
/**
* Your BSTIterator will be called like this:
* BSTIterator i = BSTIterator(root);
* while (i.hasNext()) cout << i.next();
*/