给一棵BST，注意，BST的value是一个private的东西，我们拿不到。我啥也不想说了，这题面试没写好，真得挺不开心的。
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class {
Node left;
Node right;
}
public Node nextLargest(Node node, Node root) {
if (root == null || node == null)
return null;
Node ans = null;
if (node.right != null) {
node = node.right;
while (node.left != null) {
node = node.left;
}
return node;
}
Stack<Node> s = new Stack<>();
while (root != null) {
s.push(root);
root = root.left;
}
while (!s.isEmpty()) {
Node cur = s.pop();
Node right = cur.right;
while (right != null) {
s.push(right);
right = right.left;
}
if (cur == node) {
ans = s.isEmpty() ? null : s.pop();
break;
}
}
return ans;
}
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