카타 7급 Going to the cinema

2 R

movie <- function(card, ticket, perc) {
  n <- 1
  while(TRUE) {
    a <- ticket * n
    b <- ceiling( card + ticket*perc*(1-perc^n) / (1-perc) )
    if( a > b ) break
    n <- n + 1
  }
  n
}

movie <- function(card, ticket, perc) {
  n = 1:10000
  min(which(ceiling(card + ticket * cumsum(perc^n)) < ticket * n))
}