Problem ARRTWIST

[tojra]

Please tell me the proof of the solution ARRTWIST. After searching online for hints, I found none. I only found solution, so I saw it hoping that I would get hint on implementation , etc. But solution is one liner. Can someone give me proof or atleast an intuition about that?

https://www.spoj.com/problems/ARRTWIST/

[amit9oct]

Read this:

Finding equal partial sum given two $N$-tuples of natural numbers

and

Given an array A of size n with elements from 1 to k and another Array B of size k with elements 1 to n. Show that they have a subarray of same sum.