Oozy rat in a sanitary zoo

Consider the palindromic phrase

OOZYRATINASANITARYZOO \text{OOZYRATINASANITARYZOO}

In how many ways can OOZYRATINASANITARYZOO \text{OOZYRATINASANITARYZOO} be read if you start at any O O and are restricted to read only up, down, left or right to adjacent letters?


Note: You are allowed to use the same letter twice, and you each case is counted twice since you can read a case from one direction, but it can also be read from the opposite direction.

You may use a calculator for the final step


The answer is 16744464.

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1 solution

Sharky Kesa
Oct 10, 2016

We will first count all SANITARYZOO \text{SANITARYZOO} we can make. If we focus on each quarter of the diamond grid, we find that there is 1 way to choose the S \text{S} , after which there are two choices for each letter i.e. there are 2 ways to choose an A \text{A} , after which there are two ways of choosing an N \text{N} and so forth. Since there are 11 letters in SANITARYZOO \text{SANITARYZOO} , there are 2 10 2^{10} of these in each quarter. Thus, there are 4 × 2 10 4 \times 2^{10} altogether. However, we have over-counted when the words lie along the vertical or horizontal diagonals. Thus, there are actually 4 × 2 10 4 4\times 2^{10} - 4 words. Since each of these words can be paired with any other (including itself) to create OOZYRATINASANITARYZOO \text{OOZYRATINASANITARYZOO} , there are ( 4 × 2 10 4 ) 2 = 102 0 2 = 16744474 (4\times 2^{10} - 4)^2=1020^2=16744474 total words.

Therefore, there are 16744464 16744464 total ways of reading OOZYRATINASANITARYZOO \text{OOZYRATINASANITARYZOO}

( 4 2 10 4 ) 2 (4 \cdot 2^{10} - 4)^2 is equal to 16744464, not 1040400.

Jon Haussmann - 4 years, 7 months ago

oh ! so the egoistic sharky got wrong in calculations ! :P ,

A Former Brilliant Member - 4 years, 5 months ago

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I beg your pardon? I find nothing funny in that. The answer was already updated, just not my solution.

Please refrain from insulting Brilliant members.

Sharky Kesa - 4 years, 5 months ago

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no, i am not at all insulting you, you wrote yourself in this note that you are an egoist !! link to the note , right ?

A Former Brilliant Member - 4 years, 5 months ago

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@A Former Brilliant Member How long ago was it??? Do you not think I have worked on it since then? Also, only I'm allowed to insult myself.

Sharky Kesa - 4 years, 5 months ago

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