/// <summary>
/// Algorithm that returns the next sequential node (ascending) when given a binary search tree node. Nodes in the tree have access to parent.
/// O(n) time, O(1) space
/// </summary>
/// <param name="node">BSTPNode</param>
/// <returns>BSTPNode</returns>
public static BSTPNode Successor(BSTPNode node)
{
if (node == null)
{
return(null);
}
if (node.Right != null)
{
BSTPNode currChild = (BSTPNode)node.Right;
while (currChild.Left != null)
{
currChild = (BSTPNode)currChild.Left;
}
return(currChild);
}
BSTPNode currParent = node.Parent;
if (currParent == null)
{
return(null);
}
while (currParent != null && currParent.Data < node.Data)
{
currParent = currParent.Parent;
}
return(currParent);
}
public void TestSuccessor()
{
// Arrange
// null node
BSTPNode nullNode = null;
// single node
BSTPNode singleNode = new BSTPNode(1, null);
// common case
BSTPNode commonCaseRoot = new BSTPNode(10, null);
BSTPNode commonCaseLeft = new BSTPNode(7, commonCaseRoot);
BSTPNode commonCaseLeftRight = new BSTPNode(9, commonCaseLeft);
BSTPNode commonCaseLeftRightLeft = new BSTPNode(8, commonCaseLeftRight);
BSTPNode commonCaseRight = new BSTPNode(11, commonCaseRoot);
commonCaseRoot.Left = commonCaseLeft;
commonCaseRoot.Right = commonCaseRight;
commonCaseLeft.Right = commonCaseLeftRight;
commonCaseLeftRight.Left = commonCaseLeftRightLeft;
// Act
BSTPNode nullNodeResult = TreesAndGraphs.Successor(nullNode);
BSTPNode singleNodeResult = TreesAndGraphs.Successor(singleNode);
BSTPNode commonCaseResult1 = TreesAndGraphs.Successor(commonCaseLeft);
BSTPNode commonCaseResult2 = TreesAndGraphs.Successor(commonCaseLeftRight);
BSTPNode commonCaseResult3 = TreesAndGraphs.Successor(commonCaseRight);
// Assert
Assert.IsNull(nullNodeResult);
Assert.IsNull(singleNodeResult);
Assert.AreEqual(commonCaseLeftRightLeft, commonCaseResult1);
Assert.AreEqual(commonCaseRoot, commonCaseResult2);
Assert.IsNull(commonCaseResult3);
}
public BSTPNode(int data, BSTPNode parent) : base(data)
{
Parent = parent;
}
