arrays - Ruby: creating a matrix with diagonal band of 1,2,1 -

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before start, plz understand total beginner @ ruby , computer programming, possess no prior knowledge , need programming basic of basic or else cannot understand. doing project school , stuck.

i have create code in ruby matrix n rows , n columns banded values [2,1]

[2,1,0,0,0] [1,2,1,0,0] [0,1,2,1,0] [0,0,1,2,1]

i made code dont know why wrong , where.. plz help!!

def make1d(n)   = array.new(n)    in 0..(n-1)     a[i] = 0   end   end def make2d(height,width)   = array.new(height)   in 0..(height-1)     a[i] = make1d(width)   end   end def matrixa(n)  a=make2d(n,n)   k in 0..n-2   a[k][k]=2   a[k+1][k]=1   a[k][k+1]=1   a[n-1][n-1]=2   end  end

ruby has great features can take advantage of. example, array.new takes block (do ... end) specify default value. block gets current index parameter (do |index| ... end). perfect scenario!

your logic seems quite complex setting values on diagonal. if take step back, makes diagonal special if @ row , column indices? right, equal. if go 1 diagonal right/left, row , col indices off one, , on.

so here’s how write code:

array.new(n) |row|   array.new(n) |col|     case row - col     when -1 1     when 0 2     when 1 1     else 0     end   end end

or can make shorter, , handle general case. substitute 2 value want, or make function parameter

array.new(n) |row|   array.new(n) |col|     [2 - (row - col).abs, 0].max   end end

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