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| class BSTIterator {
private final Stack<TreeNode> stack;
public BSTIterator(TreeNode root) {
this.stack = new Stack<>();
pushTreeToStack(root);
}
private void pushTreeToStack(TreeNode root) {
while (root != null) {
stack.push(root);
root = root.left;
}
}
public int next() {
TreeNode root = stack.pop();
pushTreeToStack(root.right);
return root.val;
}
public boolean hasNext() {
return !stack.isEmpty();
}
}
|
References
173. Binary Search Tree Iterator
剑指 Offer II 055. 二叉搜索树迭代器