because who needs loops?

9.R

@@ -0,0 +1,31 @@
+input <- as.numeric(readLines("input9.txt"))
+
+allplus <- function(vec) {
+    unlist(lapply(1:(length(vec) - 1), function(i) {
+                      vec[i] + vec[(i + 1):length(vec)]
+    }))
+}
+
+vvals <- sapply(1:length(input), function(x) {
+           if (x <= 25) {
+               return(TRUE)
+           }
+           tnum <- input[x]
+           l25 <- input[(x - 25):(x - 1)]
+           return(tnum %in% allplus(l25))
+           
+})
+
+inval <- input[!vvals][1]
+inval
+
+alladd <- sapply(1:(length(input) - 1), function(x) {
+           sapply((x + 1):length(input), function(y) {
+                      sel <- input[x:y]
+                      if (sum(sel) == inval) {
+                          print(sel)
+                          print(min(sel) + max(sel))
+                      }
+                      return(sum(sel))
+    })
+})