A BlackJack KOTH contest

BlackJackDavey

Boring, old fashioned c. Should compiler under ANSI or c99.

/* BlackJackDavey
 *
 * A entry for
 * http://codegolf.stackexchange.com/questions/2698/a-blackjack-koth-contest
 * copyright 2011 
 *
 * Currently expects a slightly extended version of the spec. Two
 * expected changes:
 * - Tens will be represented as 'T'
 * - The visible card string will include '#' for those cards whose
 *     *backs* we can see (slight improvement in card counting technique)
 * 
 * No disaster if neither feature is present, just sligtly degraded
 * performance.
 */
#include <stdio.h>
#include <string.h>

/* A full deck has a total value of 4*( (11*5) + (3*10) + ace ) where
 * ace is 11 or according to our need.
 **/
int fullWeight(const int current){
  int ace = (current>10) ? 1 : 11;
  return 4 * ( 11*5 + 3*10 + ace);
}
/* Return the value of a particular card in the context of our
 * current score
 */
int cardWeight(const char c, const int current){
 switch (c) {
 case '1': case '2': case '3': case '4': case '5':
 case '6': case '7': case '8': case '9':
   return (c - '0');
 case 'T': case 'J': case 'Q': case 'K':
   return 10;
 case 'A':
   return current>10 ? 1 : 11;
 }
 return 0;
}
/* returns the mean card *value* to be expected from the deck 
 *
 * Works by computing the currently unknown value and diviing by the
 * number of remaining cards 
 */
float weight(const char*known, const int current){
  int weight = fullWeight(current);
  int count=52;
  int uCount=0;
  const char*p=known;
  while (*p != '\0') {
    if (*p == '#') { /* Here '#' is a stand in for the back of a card */
      uCount++;
    } else {
      weight -= cardWeight(*p,current);
    }
    count--;
    p++;
    if ( count==0 && *p != '\0') {
      count += 52;
      weight += fullWeight(current);
    }
  }
  return (1.0 * weight)/(count+uCount);
}


int main(int argc, char*argv[]){
  int score=atoi(argv[1]);
  const char*hand=argv[2];
  const char*visible=argv[3];
  int stake=atoi(argv[4]);
  int chips=atoi(argv[5]);

  /* If current stake is less than 10, bet all the rest because a loss
     does not leave us enough to continue */
  if (chips < 10 && chips > 0) {
    printf("B %d\n",chips);
    return 0;
  }
  /* First round stategy differs from the rest of the game */
  if (strlen(hand)==2 && stake==10) {
    switch(score){
    case 10:
    case 11: /* Double down on particularly strong hands */
      if (chips >= 10) {
    printf("D\n");
    return 0;
      }
      break;
    default:
      break;
    };
  }
  /* In future rounds or when first round spcialls don't apply it is
     all about maximizing chance of getting a high score */
  if ((score + weight(visible,score)) <= 21) {
    /* if the oods are good for getting away with it, hit */
    printf("H\n");
    return 0;
  }
  /* Here odd are we bust if we hit, but if we are too low, the dealer
     probably makes it.*/
  printf("%c\n", score>14 ? 'S' : 'H');
  return 0;
}

The strategy here is documented in the comments, but is very straight ahead. Additional bets are made in only two cases (not enough stake for the next round, or double down), and this may need to change.

The game differs some from the guides offered for casino gamblers in that there is no specific information about the dealer's showing card (or can we could on that being the last entry in visible?), so some of the magic numbers are guesses.

May need some modest diddling depending on the answer to two questions in the comments.

Name from the game, my first name, and the old folk ballad.

Linear Bet

#!/usr/bin/env python
from __future__ import division
import sys
s = sys.argv

c=150    # chip modifier
f=15     # stand score

if int(s[1]) < f:
    print "H"
else:
    if int(s[4]) == 10:
        print "B", (int(s[1])/21)*c
    else:
        print "S"

This bot is a modification of the 17 strategy. This bot draws until it exceeds a score of 15 (f) and then bets int(c*(score/21)) chips. This way the bot will bet aggressively wherever possible.