Fill elements of a vector randomly depending on constraints

I have a character vector of a certain length (that should not be changed) like this:

my.vec <- rep("free", 40000)

What I need to do now is the following:

I need to loop 22 through the vector to represent an annual development (1 loop = 1 year)
in each loop 7 random elements of the vector should be changed from "free" to "occupied"
between two "occupied" elements there are supposed to stay at least 4 "free" elements (i.e. "occupied" "free" "free" "free" "free" "occupied"
if an element gets assigned "occupied" in one loop, is not available anymore for the next loops

For more clarity, here is an example with a short vector and three time steps:

# this is the intital vector:
my.vec <- rep("free", 200) 

# this is the assignment in the first three time steps:
# first time step
my.vec[c(1,25,18,10,48,41,33)] <- "occupied"
# second time step
my.vec[c(98,91,81,63,70,163,120)] <- "occupied"
# third time step
my.vec[c(199,127,150,140,172)] <- "occupied"

I hope it became clear. Anybody with an idea how to implement this?

Solution

How about this:

my.vec <- rep("free", 4000)  

# Function to check if a position can be marked 'occupied'
can_occupy <- function(vec, pos) {
  # Check boundaries and ensure at least four 'free' slots between 'occupied'
  if(pos < 1 || pos > length(vec)) {
    return(FALSE)
  }
  lower_bound <- max(1, pos - 4)
  upper_bound <- min(length(vec), pos + 4)
  # If any 'occupied' within bounds, return FALSE
  return(all(vec[lower_bound:upper_bound] == "free"))
}

for(year in 1:22) {
  occupied_this_year <- 0
  attempts <- 0  # To prevent infinite loop in case conditions can't be met
  while(occupied_this_year < 7 && attempts < 1000) {
    # Randomly select a position
    pos <- sample(length(my.vec), 1)
    if(can_occupy(my.vec, pos)) {
      my.vec[pos] <- "occupied"
      occupied_this_year <- occupied_this_year + 1
    }
    attempts <- attempts + 1
  }
  if(attempts == 1000) {
    cat("Year", year, ": Could not occupy 7 positions\n")
  }
}