The sword refers to the offer series 49--seeking 1+2+...+n and

"title" Beg 1+2+3+...+n,
* Requires no use of multiplication, for, while, if, else, switch, case and other keywords and conditional judgment statement (A? B:C).

1  PackageCom.exe10.offer;2 3 /**4 * "title" asks 1+2+3+...+n,5 * requires no use of multiplication, for, while, if, else, switch, case and other keywords and conditional judgment statement (A? B:C). 6  * @authorWGS7  *8  */9  Public classSumofn {Ten     intResult=0; One      A      Public BooleanCalcintN) { -result+=N; -         returnN!=0 && Calc (n-1);//as long as the n!=0 has been recursively performing the add operation. the     } -      -      Public intGetsum (intN) { -         if(n<0)return-1; +Calc (n);//as long as n==0 in the Calc function jumps out of the Calc function, executes the return result of the next step -         returnresult; +     } A      Public Static voidMain (string[] args) { atSumofn s=Newsumofn (); -         intN=s.getsum (-10); - System.out.println (n); -  -     } -  in}

The sword refers to the offer series 49--seeking 1+2+...+n and