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leetcode173.java
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leetcode173.java
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/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class BSTIterator {
private Stack<TreeNode> stk = new Stack<TreeNode>();
public BSTIterator(TreeNode root) {
while(root!=null){
stk.push(root);
root = root.left;
}
}
/** @return whether we have a next smallest number */
public boolean hasNext() {
return !stk.isEmpty();
}
/** @return the next smallest number */
public int next() {
TreeNode res = stk.pop();
while(res.right!=null){
stk.push(res.right);
res.right = res.right.left;
}
return res.val;
}
}
/**
* Your BSTIterator will be called like this:
* BSTIterator i = new BSTIterator(root);
* while (i.hasNext()) v[f()] = i.next();
*/