private TreeNode BuildTreeHelper(int[] preorder, int[] inorder, int preL, int preR, int inL, int inR,
Dicitionary <int, int> map)
{
if (preL > preR)
{
return(null); //base case
}
TreeNode root = new TreeNode(preorder[preL]); //create new TreeNode with current root element
int index = map[preorder[preL]]; //the index of root.val in inorder array
int numLeft = index - inL; //number of nodes at the left subtree of current root
root.left = BuildTreeHelper(preorder, inorder, preL + 1, preL + numLeft, inL, index - 1, map);
root.right = BuildTreeHelper(preorder, inorder, preL + 1 + numLeft, preR, index + 1, inR, map);
return(root);
}
private TreeNode BuildTreeHelper(int[] preorder, int[] inorder, int preL, int preR, int inL, int inR,
Dicitionary<int,int> map)
{
if(preL>preR) return null; //base case
TreeNode root = new TreeNode(preorder[preL]); //create new TreeNode with current root element
int index = map[preorder[preL]]; //the index of root.val in inorder array
int numLeft = index-inL; //number of nodes at the left subtree of current root
root.left= BuildTreeHelper(preorder, inorder, preL+1, preL+numLeft, inL, index-1, map);
root.right = BuildTreeHelper(preorder, inorder, preL+1+numLeft, preR, index+1, inR, map);
return root;
}
