Construct Binary Search Tree from Preorder Traversal.java

class Solution {
    
     public TreeNode bstFromPreorder(int[] preorder) {
        return helper(preorder, 0, preorder.length);
        
    }
    
    public TreeNode helper(int[] preorder, int rootindex, int right)
    {        
        if(rootindex >= right) return null;
        
        int value = preorder[rootindex];
        TreeNode root = new TreeNode(value);
        
        int i = rootindex+1;
	    while(i <= preorder.length-1 && preorder[i] < value)
        {
            i++;
        }
        root.left = helper(preorder, rootindex+1, i);
        root.right = helper(preorder,i, right);
        
        return root;        
    }
}