4/5 felines

bigs-and-smalls.R

numbers <- function(big = 2L, small = 6L - big) {
  stopifnot(big + small == 6L)
  c(sample(50:100, big), sample(0:49, small))
}

problem <- function(x = numbers(), parenthesis = TRUE, ns = length(x)) {
  stopifnot(all(ns > 1), all(ns <= length(x)))
  x <- as.integer(x)
  n <- if (length(ns) == 1) ns else sample(ns, 1)
  ops <- sample(c("+", "-", "/", "*"), n - 1L, TRUE)
  numbers <- sample(x, n)
  numbers <- format(numbers)
  
  if (parenthesis) {
    pinds <- sort(sample(seq_len(n), n, TRUE))
    
    odds  <- seq.int(1L, n, 2L)
    evens <- seq.int(2L, n, 2L)
    
    for (i in pinds[odds]) {
      numbers[i] <- paste0("(", numbers[i])
    }
    
    for (i in pinds[evens]) {
      numbers[i] <- paste0(numbers[i], ")")
    }
    
    if (length(evens) != length(odds)) {
      numbers[n] <- paste0(numbers[n], ")")
    }
  }
  
  form <- paste(numbers, c(ops, ""), collapse = " ")
  res <- eval(parse(text = form))
  
  attr(res, "answer") <- form
  attr(res, "vals") <- x
  
  if (!valid_solution(res)) {
    res <- problem(x, parenthesis = parenthesis, ns = ns)
  }
  
  class(res) <- "problem"
  res
}

solution <- function(x = numbers(), answer, ns = length(x)) {
  stopifnot(valid_solution(answer))
  answer <- as.integer(answer)
  repeat {
    res <- problem(x, ns = ns)
    if (res == answer) break
    form <- paste(attr(res, "answer"))
    form <- format(form, width = 35)
    ans <- format(as.integer(res), width = 3)
    cat(form, " = ", ans, "\n", sep = "")
    Sys.sleep(.25)
  }
  
  attr(res, "answer")
}

valid_solution <- function(x) {
  isTRUE(x %% 1 == 0 & x >= 0 & x <= 999)
}

print.problem <- function(x, ...) {
  print(as.integer(x))
  invisible(x)
}

x <- c(25, 50, 3, 10, 2, 1)
x <- c(25, 50, 3, 2, 1)
system.time(message(solution(x, 834, ns = 5), " = 834"))

x <- c(100, 25, 75, 50, 4, 3)
system.time(message(solution(x, 797), " = 797"))