I was giving online exam on hackerearth. The problem statement is 
Note: It has already ended few days back.
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At first, I thought of using polynomial rolling hash function. But since we have integral values, there will be high probability of collision. So, couldn't able to verify its truthfulness.
I can't come up with a better solution, but I think you can use suffix array to compare 2 substrings in O(log(n)) instead of hash. Nevertheless, hash still works pretty well if you use 2/3 mods. (and seems to be easier to implement too?)
I solved it using the above solution during contest and it passed all tests :)
In the contest, I submitted a brute force solution and even that passed, which means that test cases were quite weak.
Very true, I was doubtful that hashing would work, then I thought oh wait I am on hackerearth not on codeforces, walla ac, lol.
Still I guess double hashing or triple hashing would reduce the collision probability.