# minimum number of square tiles needed to tile a square floor

I was solving one assignment and I am not getting ideas for this, I tried thinking in terms of dp but couldn’t think of optimal substructure. It goes like this :-
I need to find a minimum number of square tiles of dimension less than the dimension of floor given needed to tile that floor, example:-

1. for a floor of dimension n=4 we have tiles of size 1, 2, 3. so 4 tiles of 2*2 will do, I suppose that is minimum;
2. Another thing is we may have any number of non-optimal solution to this problem, say for n=4 we may have a tile of 3by3 and 7 tiles of 1by1 i.e. total 8 tiles. I also need to count the number of non-optimal unique solutions (ie. same configuration should not be counted twice).
I am attaching a scerenshot for clarity
Any help is appreciated…

Well, it is an assignment.

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Before asking for help in Assignments, show us what you have done till now in achieving your goal.

Asides that, I think the answer will always be 4 in case the edge is even. Didn’t think about the case when edge will be odd.

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well I think as utkarsh1997 said that in case of even length edge it will be 4 as it can be symmetrically divided by the tiles half it’s edges length.
And In case of odd edge length tile I think it should be 4+floor(n/2)2
that is because it can be divided into 1 tile of size ceil(n/2), 3 tiles of floor(n/2) and 2
floor(n/2) tiles of edge size 1 I think thats the only way we can divide tiles minimally.
Let me know if you can divide with less tiles than I showed.

Hulk, try this and tell if this formula yields correct result for optimal solution-
Let n be dimension of square floor-

For even numbers-

gcd(n,n)=n/2 (since n is excluded)

Ans = (n x n)/[n/2 x n/2] = 4.

For Odd NON-PRIME numbers-

Let k be gcd of n, such that k*l = n.

Try this formula-

Number of squares = 1+ [ n x n - [k x (l-1)]^2 ]/(k x k)

For n=9, this gives-
No of squares = 1+ (81- [3*2]^2 )/9

= 1+ (81-36)/9
=1+5
=6.

FOR ODD PRIME NUMBERS-

Number of Squares follows a pattern-

3-6
5-8
7-9
11-11
13-12


Pattern is +2,+1,+2,+1 (+2 if n+1 is divisible by 4, else +1 )

Check it with your results, I am not that good at finding minimum number of X lol.
(PPS: Mid sems ended today, WEW. Some time for coding now :3 )

For a composite number n you can consider the problem identical to the problem for side length equal to the smallest prime divisor of n. Let n = a\times b where a is the smallest prime divisor of n. Then you can consider the n \times n block as an a \times a block where each unit tile is of dimension b \times b. This is the best way I have come up with for reducing n, but I am not completely sure this is the absolute best way. Also after doing such a reduction I am stuck with a prime n for which I can find no strict approach
This is a very intriguing problem by the way… will probably give me sleepless nights.

Correction: I realized it is not proper to use the term smallest prime divisor. Actually it is the smallest divisor of n excluding 1 (as dimension of usable tiles < n). This divisor will naturally always be prime. So the answer for a composite n is the same as the answer for its smallest divisor excluding 1, according to my proposition.

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The 3*3 tile can be placed at any of 4 corners.
They have to be counted same or different?
I am guessing they are same.

@prakhariitd I have edited the problem, please see it.

@vijju123, did you delete the whole answer?

Yes. I am unable to understand the Q, so I decided its better not to cause confusions.

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what part of question you did not understand ?

Nevermind, I get the Q. Sorry, I cant help in this one bro. (And lol, I am feeling like “why did I wrote that answer in first place”. God! This is what mid-sem exams does to a poor guy like me XD. Sorry for whatever nonsense I might have babbled, lets say, I was not under the best mindset yesterday.

Lol. Nailed it dude XDDD. I was like, preparing for tomorrows exam and I read it and I was like “LOL XDDD”. (PS: No offence to anyone intended. Just telling that this thing cracked me up XD)

does that mean that if somebody can’t solve an assignment, then they can’t ask also.

I have updated the problem, I have tried in terms of dp but could not think of an optimal substructure, What can one I when I don’t have an approach. For even part it seems alright, but it is the case of prime numbers where the main problem lies.

and I see you have not said anything about the earlier answer you gave @prakhariitd. you can let me know if I have not correctly understood your answer.

Prime numbers or odd numbers in general?

@vijju123 glad it could made you laugh in stress time

@paras17jain, I feel that merely a formula won’t do your formula does not satisfy for n=7, your answer says 10 but I can fit this into 9 tiles

of sizes 4 , 3 ,3 . 2, 2, 2 , 1, 1 , 1, I will post a diagram later , try fitting these tiles.

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Assuming gcd does stand for Greatest Common Divisor, gcd(n,n)=n. How can it be n/2?