發送短信 : Unique sums and differences in finite Abelian groups

 _    _      ___      _____    _    _             
| || | ||   / _ \\   |__  //  | || | ||     ___   
| || | ||  / //\ \\    / //   | || | ||    /   || 
| \\_/ || |  ___  ||  / //__  | \\_/ ||   | [] || 
 \____//  |_||  |_|| /_____||  \____//     \__ || 
  `---`   `-`   `-`  `-----`    `---`       -|_|| 
                                             `-`