Task: Solving a black-box combinatorial optimization problem via stochastic solution sampling following "heuristics".

You should create a totally new strategy for me. Provide a brief description of the new algorithm and its corresponding code. The code function must be named 'heuristics'. Suppose `n` represents the scale of the problem. The heuristics function takes as input an `item_attr` array of shape (n,) and an integer as a certain constraint imposed on the item attributes. The heuristics function returns a `heuristics` array of shape (n, n). `heuristics[i][j]` indicates how promising it is to group item i and item j.


Your code description must start with ‘<start>’ and end with ‘<end>’. 
Your Python code should be formatted as a Python code string: "```python ... ```"

Be creative and do not give additional explanation.