two multidimensional array handling in ruby

I've got an array like this

[["1"], ["2","3"]]

In the beginning I had this algorithm

maxarray = []
i = 0
m = array.count
while i < m do
  x = 0
  s = array[i].count
  while x < s do
    maxarray[i][x] = (Integer(array[i][x]) + [Integer(maxarray[i-1][x-1]), Integer(maxarray[i-1][x])].max)
    开发者_高级运维x+=1 
  end
  i+=1
end

the error was this:

`<main>': undefined method `[]' for nil:NilClass (NoMethodError)

so I thought maybe the array indexes goes wrong so I extended my algorithm

maxarray = []
i = 0
m = array.count
while i < m do
  x = 0
  s = array[i].count
  while x < s do
    if i-1 < 0 
        item2 = 0
    elsif i-1 < 0 && x-1 < 0 
        item1 = 0
    else item1 = maxarray[i-1][x-1] 
         item2 = maxarray[i-1][x] 
    end
    maxarray[i][x] = (Integer(array[i][x]) + [Integer(item1), Integer(item2)].max)
    x+=1 
  end
  i+=1
end

but now i have an different error:

`Integer': can't convert nil into Integer (TypeError)

how can prevent this error and run the script?

Why you don't flatten the array and make your computing? Certainly it will make your function simplier.