code: func (c *CMSketch) MergeCMSketch(rc *CMSketch) error {
  	if c.depth != rc.depth || c.width != rc.width {
  		return errors.New("Dimensions of Count-Min Sketch should be the same")
  	}
  	if c.topN != nil || rc.topN != nil {
  		return errors.New("CMSketch with Top-N does not support merge")
  	}
  	c.count += rc.count
  	for i := range c.table {
  		for j := range c.table[i] {
  			c.table[i][j] += rc.table[i][j]
  		}
  	}
  	return nil
  }
docs: // MergeCMSketch merges two CM Sketch.
  // Call with CMSketch with Top-N initialized may downgrade the result