In Order Successor in Binary Search Tree

Question

Given a node in a BST, how does one find the next higher key?

Answer 1

Node successor(int data) {
  return successor(root, data);
}

// look for the successor to data in the tree rooted at curr
private Node successor(Node curr, int data) {
  if (curr == null) {
    return null;
  } else if (data < curr.data) {
    Node suc = successor(curr.left, data);
    // if a successor is found use it otherwise we know this node
    // is the successor since the target node was in this nodes left subtree
    return suc == null ? curr : suc;
  } else if (data > curr.data) {
    return successor(curr.right, data);
  } else {
    // we found the node so the successor might be the min of the right subtree
    return findMin(curr.right);
  }
}

private Node findMin(Node curr) {
  if (curr == null) {
    return null;
  }

  while (curr.left != null) {
    curr = curr.left;
  }

  return curr;
}