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Copy path105-ConstructBinaryTreeFromPreorderAndInorderTraversal.cs
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105-ConstructBinaryTreeFromPreorderAndInorderTraversal.cs
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//-----------------------------------------------------------------------------
// Runtime: 100ms
// Memory Usage: 26.4 MB
// Link: https://leetcode.com/submissions/detail/378628320/
//-----------------------------------------------------------------------------
namespace LeetCode
{
public class _105_ConstructBinaryTreeFromPreorderAndInorderTraversal
{
public TreeNode BuildTree(int[] preorder, int[] inorder)
{
if (preorder.Length == 0 || inorder.Length == 0) return null;
return BuildTree(preorder, 0, preorder.Length, inorder, 0, inorder.Length);
}
private TreeNode BuildTree(int[] preorder, int preorderStart, int preorderEnd, int[] inorder, int inorderStart, int inorderEnd)
{
var root = new TreeNode(preorder[preorderStart]);
var inorderIndex = inorderStart;
for (; inorderIndex < inorderEnd; inorderIndex++)
if (inorder[inorderIndex] == preorder[preorderStart])
break;
var leftLength = inorderIndex - inorderStart;
if (leftLength > 0)
root.left = BuildTree(preorder, preorderStart + 1, preorderStart + 1 + leftLength, inorder, inorderStart, inorderIndex);
if (inorderEnd > inorderIndex + 1)
root.right = BuildTree(preorder, preorderStart + 1 + leftLength, preorderEnd, inorder, inorderIndex + 1, inorderEnd);
return root;
}
}
}