No body gave solutions though in these questions and in the 1st link the solution given is n^2 which won’t work.
Yes, I mailed them.
Any type of Reply?
Not yet. No reply. I’ll tell you when I receive it.
That was a nice one 
CodeChef should NOT(and will NOT, as @errichto said) remove a question from a contest after it’s ended.
If it would have been during the contest, they could have done it. But removing the entire problem now would be unfair for most of the people who actually spent a lot of time thinking.
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THANKS FOR CONFIRMATION!! Q getting deleted after contest would put people off as “who knows I may spend hours solving this and it wont count in the end…” because as you rightly remarked, cheating in online contest is tough to eradicate completely. I simply hope that the decision you all take results in best of all of us. Thanks one again!! 
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swetankmodi is right. That’d be unfair to many more. It’d do more harm than good.