再用n2的时间（两重循环）枚举d-c，并将b-c的值作为键，在Hash数组中查找是否存在。如果能找到essential相同的node点，则找到了一组满足 d-c = a+b的值。（注意检查a b c d 四个数不重复） Standard screening and adjustment of salinity concentrations are crucial for the nicely-becoming of one's marine life. Always use a reliable hydrometer or refractometer to evaluate salinity accurately. गड़बड़िया... https://pearlaquatics.my/product-category/tester/