Binary Search Tree Iterator
Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.
Calling
next() will return the next smallest number in the BST.
Note:
next() and hasNext() should run in average O(1) time and uses O(h) memory, where h is the height of the tree.
---------------------------------------------- think ------------------------------------------------------------
in-order traversal
the usage of vector as stack
---------------------------------------------- codes --------------------------------------------------------------
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
private:
vector<TreeNode*> stack;
public:
BSTIterator(TreeNode *root) {
while(root) {
stack.push_back(root);
root = root->left;
}
}
/** @return whether we have a next smallest number */
bool hasNext() {
if (stack.size()) {
return true;
} else {
return false;
}
}
/** @return the next smallest number */
int next() {
TreeNode* nxt = stack.back();
stack.pop_back();
assert(nxt);
int result = nxt->val;
if (nxt->right) {
stack.push_back(nxt->right);
nxt = nxt->right;
nxt = nxt->left;
while (nxt) {
stack.push_back(nxt);
nxt = nxt->left;
}
}
return result;
}
};
/**
* Your BSTIterator will be called like this:
* BSTIterator i = BSTIterator(root);
* while (i.hasNext()) cout << i.next();
*/
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