Problem 1130. Challenging perms function!

Created by Mehmet OZC

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This problem is highly related with <a href="http://www.mathworks.com/matlabcentral/cody/problems/1127-decrypt-a-secret-message">Problem 1127</a>.In oder to encrypt the word 'go' using phone keyboard, we need to do these;- first find the digits that includes the letters in word. For example letter 'g' takes place on key 4. Letter 'o' is on key 6. So first number is 46.- create all string permutations using the letters on keys (4 and 6). There are 'ghi' letters on key 4 and 'mno' letters on key 6. All two letter permutation list is {'gm';'gn';'go';'hm';'hn';'ho';'im';'in';'io'}. In this list third one is 'go'. So second number must be 3.If input is 'go'; output must be [46 3].What about 'hydroglycerin'? it is 1679616 th word on the permutation list constructed using keys 4937645923746.If input is 'hydroglycerin'; output must be [4937645923746 1679616].Given a string, return the keys on phone-keyboard and the order of this string in permutation list!

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Last Solution submitted on Oct 02, 2020

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3 Comments

Richard Zapor on 24 Dec 2012

The test set gives a false impression as to Matlab's large number precision. For the case of x = 'antidisestablishmentarianism';
y_correct = [2684347378225474636827426476 13474859120710];
The eps(2684347378225474636827426476) is 5.4976e+11. An input of 'antidisestablishmentarianist' will return y_correct = [2684347378225474636827426478 13474859120710]; However, the ism y_correct would score the ist correct as Matlab cannot distinguish the two huge values. A vector output of the first part is one method to get unique solutions. A second method would require uint64 and having multiple values. I like the pairing of encryption and decryption challenges.
Nice Challenge.

Mehmet OZC on 26 Dec 2012

I understand. Thanks for the comment.

Rafael S.T. Vieira on 2 Oct 2020

Mehmet, what Richard tried to say is that 2684347378225474636827426476 is a number greater than 2^64-1, the highest unsigned integer number that MATLAB can store with precision (which means storing this number in double will make it loose its less significant digits). Therefore, the 5th case cannot be compared exactly with the function isequal. You must use some tolerance when comparing such numbers, abs(x-y) < tol, or use characters for an exact solution, like '2684347378225474636827426476'.

PS: And any solutions generating this number by any means are not correct at all, inclunding mine. We are all trying to store 3GB in a 2GB pendrive, it will not store everything.

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Problem 1130. Challenging perms function!

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Problem 1130. Challenging perms function!

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