2023 - day 09

head(txt)

[1] "13 9 1 2 50 233 728 1871 4300 9258 19218 39107 78571 155948 304911 585118 1098671 2014751 3605471 6296784 10739208"       
[2] "16 39 84 173 354 719 1433 2795 5379 10350 20134 39782 79679 160823 324893 652941 1299026 2548741 4917680 9311783 17280520"
[3] "0 14 39 74 117 165 221 322 616 1545 4242 11327 28389 66554 146616 305124 602288 1130037 2015139 3405883 5420809"          
[4] "6 14 26 55 130 298 626 1203 2142 3582 5690 8663 12730 18154 25234 34307 45750 59982 77466 98711 124274"                   
[5] "15 27 57 112 193 306 501 952 2094 4836 10868 23071 46018 86517 154090 261201 422937 655705 974331 1386730 1885055"        
[6] "4 12 28 52 84 124 172 228 292 364 444 532 628 732 844 964 1092 1228 1372 1524 1684"                                       

Part I

Continue series of numbers by differencing. Add one more element and submit sum of these extrapolated values.

R

lapply(
  txt
  , FUN = \(i){
    # i = txt[1]
    l = strsplit(i, split = " ")[[1]] |> 
      as.integer() |> 
      list()
    
    while (sum(abs(l[[1]])) > 0L){
      l = c(list(diff(l[[1]])), l)
    }

    incr = integer(length(l))
    incr[1] = 0
    
    for (k in seq_along(l)){
      l[[k]] = c(l[[k]], l[[k]][length(l[[k]])] + incr[k])
      incr[k + 1] = l[[k]][length(l[[k]])]
    }
    
    l[[length(l)]][length(l[[length(l)]])]
     
  }
  
) |> 
  unlist() |> 
  sum()

[1] 1987402313

Python

Part II

Add \(m\) successive cards where \(m\) is the number of matches in a card. Get the final number of cards.

R

Python