private int FindInorderIndexByValue(int[] inorder, SubTreeSpan inorderSpan, int targetVal)
{
for (int i = inorderSpan.StartIndex; i <= inorderSpan.EndIndex; i++)
{
if (inorder[i] == targetVal)
{
return(i);
}
}
throw new ArgumentException($"Can not find target value in given inorder span. Target value is {targetVal}", nameof(targetVal));
}
private TreeNode BuildSubTree(int[] inorder, SubTreeSpan inorderSpan,
int[] postorder, SubTreeSpan postorderSpan)
{
if (inorderSpan.StartIndex == inorderSpan.EndIndex)
{
if (inorder[inorderSpan.StartIndex] == postorder[postorderSpan.EndIndex])
{
return(new TreeNode(inorder[inorderSpan.StartIndex]));
}
else
{
throw new ArgumentException();
}
}
else if (inorderSpan.StartIndex > inorderSpan.EndIndex)
{
return(null);
}
var rootVal = postorder[postorderSpan.EndIndex];
var rootNode = new TreeNode(rootVal);
var subtreeDivider = FindInorderIndexByValue(inorder, inorderSpan, rootVal);
rootNode.left = BuildSubTree(
inorder,
new SubTreeSpan(inorderSpan.StartIndex, subtreeDivider - 1),
postorder,
new SubTreeSpan(postorderSpan.StartIndex, postorderSpan.StartIndex + subtreeDivider - inorderSpan.StartIndex - 1));
rootNode.right = BuildSubTree(
inorder,
new SubTreeSpan(subtreeDivider + 1, inorderSpan.EndIndex),
postorder,
new SubTreeSpan(postorderSpan.StartIndex + subtreeDivider - inorderSpan.StartIndex, postorderSpan.EndIndex - 1));
return(rootNode);
}
