risk.R

risk_attack_succeed_sim <- function(attack, defend){
  while(attack >= 2 && defend > 0){
    n_attack <- min(c(3, attack - 1))
    n_defend <- min(c(2, defend))
    
    roll_attack <- sample(1:6, n_attack, replace = TRUE)
    roll_defend <- sample(1:6, n_defend, replace = TRUE)
    
    n_compare <- min(c(n_attack, n_defend))
    
    roll_attack <- sort(roll_attack, decreasing = TRUE)[seq_len(n_compare)]
    roll_defend <- sort(roll_defend, decreasing = TRUE)[seq_len(n_compare)]
    
    win_defend <- sum(roll_attack <= roll_defend)
    
    attack <- attack - (win_defend)
    defend <- defend - (n_compare - win_defend)
  }
  
  defend == 0
}


risk_prob_win <- function(attack, defend, rep){
  sum(replicate(rep, risk_attack_succeed_sim(attack, defend))) / rep
}

risk_prob_win(2, 1, 1000)