Method recur

RecoveraTreeFromPreorderTraversal.java:25–46

(String traversal, int depth)

        return recur(traversal,0);
    }
    public TreeNode recur(String traversal, int depth){
        if(index >= n) return null;
        //count the dash
        int count=0;
        int tempI=index;
        while(tempI < n && !Character.isDigit(traversal.charAt(tempI))){
            count++;
            tempI++;
        }
        if(count!=depth) return null;
        index = tempI;
        //find the number
        int val=0;
        while(index < n && Character.isDigit(traversal.charAt(index))){
            val = val * 10 + (traversal.charAt(index) - '0');
            index++;
        }
        TreeNode node = new TreeNode(val);
        node.left = recur(traversal, depth+1);
        node.right = recur(traversal, depth+1);
        return node;
    }

}