[leetcode] Construct Binary Tree from Inorder and Postorder Traversal

public class Solution {
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        if (postorder.length == 0 || inorder.length == 0)
            return null;
        TreeNode res = build(inorder, postorder, inorder.length);
        return res;
    }

    private TreeNode build(int[] in, int[] post, int len) {
        if (len <= 0)
            return null;
        TreeNode root = new TreeNode(post[len - 1]);
        int idx = -1;
        for (int i = 0; i < len; i++) {
            if (in[i] == post[len - 1])
                idx = i;
        }

        root.left = build(Arrays.copyOfRange(in, 0, idx), Arrays.copyOfRange(post, 0, idx), idx);
        root.right = build(Arrays.copyOfRange(in, idx + 1, len), Arrays.copyOfRange(post, idx, len - 1), len - 1 - idx);

        return root;
    }
    

    public static void main(String[] args) {
        new Solution().buildTree(new int[] { 9, 3, 15, 20, 7 }, new int[] { 9, 15, 7, 20, 3 });
    }
}