Construct Binary Tree from Inorder and Postorder Traversal

    //iterative
    public TreeNode buildTree(int[] inorder, int[] postorder) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(inorder.length == 0 || inorder.length != postorder.length) return null;
        return buildTree(inorder, postorder, 0, inorder.length - 1, 0, inorder.length - 1);
    }
    
    public TreeNode buildTree(int[] inorder, int[] postorder, int instart, int inend, int poststart, int postend) {
        if(poststart > postend || instart > inend) return null;
        if(poststart == postend) return new TreeNode(postorder[poststart]);
        TreeNode root = new TreeNode(postorder[postend]);
        int index = instart;
        while(index <= inend && inorder[index] != root.val) index++;
        root.left = buildTree(inorder, postorder, instart, index - 1, poststart, poststart + index - instart - 1);
        root.right = buildTree(inorder, postorder, index + 1, inend, poststart + index - instart, postend - 1);
        return root;
    }