public void PostOrderTraverse(TreeNode node)
{
if (node == null) return;
PostOrderTraverse(node.left);
PostOrderTraverse(node.right);
Console.Write(node.val + " ");
}
private TreeNode BuildTree(int[] preorder, int preLeftIdx, int preRightIdx, int[] inorder, int inLeftIdx, int inRightIdx)
{
TreeNode root = new TreeNode(preorder[preLeftIdx]);
//find root index in inorder
int rootOfIn = -1;
for (int i = inLeftIdx; i <= inRightIdx; i++)
{
if (inorder[i] == root.val)
{
rootOfIn = i;
break;
}
}
//find left sub
int noOfNodeInSubLeft = rootOfIn - inLeftIdx;
if (noOfNodeInSubLeft == 0)
{
root.left = null;
}
else
{
root.left = BuildTree(preorder, preLeftIdx + 1, preLeftIdx + noOfNodeInSubLeft, inorder, inLeftIdx, inLeftIdx + noOfNodeInSubLeft - 1);
}
//find right sub
int noOfNodeInSubRight = inRightIdx - rootOfIn;
if (noOfNodeInSubRight == 0)
{
root.right = null;
}
else
{
root.right = BuildTree(preorder, preRightIdx - noOfNodeInSubRight + 1, preRightIdx, inorder, inRightIdx - noOfNodeInSubRight + 1, inRightIdx);
}
return root;
}
static void Main(string[] args)
{
TreeNode root = new TreeNode(1);
TreeNode n1 = new TreeNode(2);
TreeNode n2 = new TreeNode(3);
root.left = n1;
root.right = n2;
TreeNode n3 = new TreeNode(4);
TreeNode n4 = new TreeNode(5);
TreeNode n7 = new TreeNode(6);
n1.left = n3;
n1.right = n4;
n2.left = n7;
Program p = new Program();
//p.PreOrderTraverse(root);
//Console.WriteLine();
//p.InOrderTraverse(root);
//Console.WriteLine();
//p.PostOrderTraverse(root);
//Console.WriteLine();
int[] preorder =
{1,2,4,5,3,6 };
int[] inorder =
{4,2,5,1,6,3 };
//{ 1, 2, 3, 4 };
int[] postorder =
{ 4,5,2,6,3,1 };
//{ 1, 4, 3, 2 };
TreeNode preTree = p.BuildTree(preorder, inorder);
p.PreOrderTraverse(preTree);
Console.WriteLine();
Console.ReadKey();
}
