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） Permit another champion the rest of your aquatic realm, reducing gravel hazards and preserving the pristine perfection of the acrylic haven. Dive into your TRUVU method—safeguard your tank, banish algae, and rev... https://pearlaquatics.my/trade-in-used-aquarium/