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[LeetCode]173 Binary Search Tree Iterator
https://oj.leetcode.com/problems/binary-search-tree-iterator/
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class BSTIterator {
//
// NOTE
// After the iterator built, if we modify the original tree,
// Ideally we should throw ConcurrentModificationException
// But this need some special logic when modify tree.
//
// In this case, we just make assumption that
// The iterator won‘t be effected after being built.
public BSTIterator(TreeNode root) {
// Validate
stack = new Stack<>();
pushAllLefts(root);
}
/** @return whether we have a next smallest number */
// O(1) time
// O(h) space
public boolean hasNext() {
return !stack.empty();
}
/** @return the next smallest number */
// O(h) time
// O(h) space
public int next() {
// Assume hasNext() == true.
//
// A Inorder visiting
TreeNode min = stack.pop();
// Can be done async
pushAllLefts(min.right);
return min.val;
}
private void pushAllLefts(TreeNode node)
{
while (node != null)
{
stack.push(node);
node = node.left;
}
}
private Stack<TreeNode> stack;
}
/**
* Your BSTIterator will be called like this:
* BSTIterator i = new BSTIterator(root);
* while (i.hasNext()) v[f()] = i.next();
*/[LeetCode]173 Binary Search Tree Iterator
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