PROBLEM LINK:
Practice
Contest: Division 1
Contest: Division 2
Contest: Division 3
Contest: Division 4
Author: raysh07
Tester: iceknight1093
Editorialist: iceknight1093
DIFFICULTY:
TBD
PREREQUISITES:
None
PROBLEM:
Alice has A cookies, Bob has B, where A \gt B.
Is it possible for Alice to give some cookies to Bob so that they have an equal number of cookies?
If yes, how many should she give him?
EXPLANATION:
The total number of cookies between Alice and Bob is A+B.
If they must have an equal number of cookies, then each person must have
cookies.
If A+B is an odd number, then \frac{A+B}{2} is not an integer, so such a distribution is impossible.
So, the answer is -1 in this case.
If A+B is an even number, it’s possible for a valid distribution to exist.
Alice has A cookies, and wants to end up with \frac{A+B}{2}.
This means she must give away
cookies, which is the answer.
TIME COMPLEXITY:
\mathcal{O}(1) per testcase.
CODE:
Editorialist's code (PyPy3)
a, b = map(int, input().split())
if (a+b)%2 == 1: print(-1)
else: print((a-b)//2)