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seen Mar 17 '13 at 23:05

Mar
17
awarded  Commentator
Mar
17
comment Inclusion Exclusion combinatorics 101 question
Brian, after reviewing your answer I have a question about the 1+x2+x3=4 part. As you basically want to exclude cases where there are 14 per x, how excluding x1 + x2 + x3 = 4 (which basically distributing 4 over x's, including case of x1=1, x2=3 and so on) helps you here? Thanks again.
Mar
4
comment Recursive combinatorics with numbers and operators
That's exactly my question (probably of whole recurrence idea) - if it included in (n-1), it will be included in following (n-i)? I.e. the only option to take a case with different situation? What about cases where the situation would be the same (i.e. string of only digits with no limitations)? Thanks for any clarification on this.
Mar
4
comment Recursive combinatorics with numbers and operators
Sorry - missed term from original question, saying that strings also can't end on an operator (though the answer remains the same). The bit you mentioning: "arbitrary string of length n−2 followed by two digits, those are being counted correctly in the first case" - this the bit I don't fully understand (probably as part of whole recurrence idea): if I counted the (n-1) ending on digit, why I should not count it again for (n-2) - but only the case of digit/operator? I.e. does counting something at (n-1), automatically counts all subsequent (n-i), and counting it again will be a duplicate?
Mar
4
revised Recursive combinatorics with numbers and operators
added 10 characters in body
Mar
2
comment Recursive combinatorics with numbers and operators
Question, why we don't take into account the case of: A valid sequence, followed by one of 0 or 1, and one of 0 or 1
Mar
2
comment Recursive combinatorics with numbers and operators
I've reviewed this question again, and see I still not fully get it - namely, why we don't take into account the case of f(n-2),0/1,0/1 (digit and digit again)?
Feb
26
comment Recursive combinatorics with numbers and operators
Thanks for the effort, though joriki answer did the click for me.
Feb
26
comment Recursive combinatorics with numbers and operators
Thanks for the answer, it specifically pointed I misunderstood the recursive concept, by treating it like a recursive function processing input from the start, rather then a decreasing series.
Feb
24
comment Recursive combinatorics with numbers and operators
Thanks for your remark, clarified.
Feb
24
awarded  Informed
Feb
23
revised Recursive combinatorics with numbers and operators
added 70 characters in body; edited title
Feb
23
asked Recursive combinatorics with numbers and operators
Feb
2
asked Inclusion Exclusion combinatorics 101 question
Feb
2
comment Finding recurrence relations in combinatorics
Thanks for the great explanation!
Feb
2
awarded  Scholar
Feb
2
accepted Finding recurrence relations in combinatorics
Feb
2
comment Basic inclusion exclusion problem - picking 24 balls out of four sets of 10 balls
Just to understand, the second inclusion will be of 6(4 1) + 6(3 1) + 6(2 1) + 6(1 1) - correct? Thanks!
Feb
1
awarded  Editor
Feb
1
awarded  Supporter