BALLSUM - Ball sum

You have a bag filled with N balls.Each Ball has a distinct number from 1 to N printed on it.All the numbers are distinct. You withdraw two balls from the bag and take their sum. You need to calculate the probability that the sum is not greater than the given number K(<=N). The Answer should be displayed in the form of p/q.(except when the answer is 0 or 1)


Input consists of various test cases. Each test case consist of two integer inputs,N and K. (0<=K<=N<=1000000000) The program stops taking input when N and K equals -1


Output the result in the form of p/q.(Except when the answer is 0 or 1)


3 2
100 5
10 6
-1 -1


hide comments
fuadul_hasan: 2020-06-25 10:42:51

ohh.....! at last i have done it

letuantam96: 2019-03-13 08:54:19

phewwww. finally AC
be careful with extralarge number, u may need long long int type

sagar_june97p: 2019-01-02 17:20:53

Last edit: 2019-01-02 17:22:31
kushagra_2: 2018-12-14 14:06:04

got it in O(1) :) easy problem needs gcd!!!

anirudnits: 2018-04-25 08:48:01

Got 4 WA's and finally an AC with the same code!!!

flyingduchman_: 2018-04-10 12:35:00

Note that K <= N.

Last edit: 2018-04-22 08:11:52
hello_world123: 2018-03-15 11:08:24

getting tle

srinu_viratian: 2018-01-11 14:55:13

for n=k=0=1
what will be the output?

bayulaxana: 2017-12-29 17:45:39

Very Nice problem...
It consist of mathematics, also GCD.
AC in one go :)

jha4032: 2017-12-27 13:01:56

O(1).............. :)

Added by:Prateek Agarwal
Time limit:1s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: ASM64 GOSU JS-MONKEY