code: public void add(int id, float c) {
  		int p = Arrays.binarySearch(index, id);
  		if (p >= 0) {
  			data[p] = ((float) data[p]) + c;
  		} else {
  			put(id, c);
  		}
  	}
docs: 对应位置加上值: x[i] = x[i]+c
  
  @param id
  @param c