19

# problem 19
binary_search <- function(vector, element, start = 1, end = length(vector)) {
  if (end < start)
    return(NaN)
  m <- as.integer(ceiling((end + start) / 2)) # Midpoint
  # Элемент слева
  if (vector[m] > element) {
    binary_search(vector, element, start = start, end = m - 1L)
  }
  # Элемент справа
  else if (vector[m] < element) {
    binary_search(vector, element, start = m + 1L, end = end)
  }
  # Элемент найден
  else
    return(m)
}

binary_search(c(1, 2, 3, 4,4,4,4, 5, 6, 7, 8, 9, 10), 5)