codeiq.coffee

# 問題: 5, 6, 7, 8, 9, 1, 0, 1, 1, 1, 2, 1, 3, ... 
# という数列のn番目の数字を求める関数を書け

f = (n) -> n + 5

solve = (index)->
  ret = ""
  cnt = 0
  while true
    ret += f(cnt++)
    if ret.length > index
      return ret[index]

solve2 = (index,n,acc) ->
  if n == undefined 
    return solve2(index + 4,0,0)
  next_n = n + 1
  next_acc = acc + 9 * next_n * Math.pow(10,n)
  if index < next_acc
     tmp = index - acc
     mod = tmp % next_n  
     div = tmp / next_n
     return (div + Math.pow(10,n)).toString().charAt(mod)
  else 
    solve2(index,next_n,next_acc)

console.log [0..10].map (i) -> solve2 i
console.log [0..10].map (i) -> solve i

alert 'answer solve : ' + solve2(Math.pow(10,7))
alert 'answer solve : ' + solve(Math.pow(10,7))