Task

Write a player of the Bulls and Cows game, rather than a scorer. The player should give intermediate answers that respect the scores to previous attempts.

One method is to generate a list of all possible numbers that could be the answer, then to prune the list by keeping only those numbers that would give an equivalent score to how your last guess was scored. Your next guess can be any number from the pruned list.

Either you guess correctly or run out of numbers to guess, which indicates a problem with the scoring.



Related tasks

   Bulls and cows
   Guess the number
   Guess the number/With Feedback (Player)


#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
 
char *list;
const char *line = "--------+--------------------\n";
int len = 0;
 
int irand(int n)
{
	int r, rand_max = RAND_MAX - (RAND_MAX % n);
	do { r = rand(); } while(r >= rand_max);
	return r / (rand_max / n);
}
 
char* get_digits(int n, char *ret)
{
	int i, j;
	char d[] = "123456789";
 
	for (i = 0; i < n; i++) { 
		j = irand(9 - i);
		ret[i] = d[i + j];
		if (j) d[i + j] = d[i], d[i] = ret[i];
	}
	return ret;
}
 
#define MASK(x) (1 << (x - '1'))
int score(const char *digits, const char *guess, int *cow)
{
	int i, bits = 0, bull = *cow = 0;
 
	for (i = 0; guess[i] != '\0'; i++)
		if (guess[i] != digits[i])
			bits |= MASK(digits[i]);
		else ++bull;
 
	while (i--) *cow += ((bits & MASK(guess[i])) != 0);
 
	return bull;
}
 
void pick(int n, int got, int marker, char *buf)
{
	int i, bits = 1;
	if (got >= n)
		strcpy(list + (n + 1) * len++, buf);
	else
		for (i = 0; i < 9; i++, bits *= 2) {
			if ((marker & bits)) continue;
			buf[got] = i + '1';
			pick(n, got + 1, marker | bits, buf);
		}
}
 
void filter(const char *buf, int n, int bull, int cow)
{
	int i = 0, c;
	char *ptr = list;
 
	while (i < len) {
		if (score(ptr, buf, &c) != bull || c != cow)
			strcpy(ptr, list + --len * (n + 1));
		else
			ptr += n + 1, i++;
	}
}
 
void game(const char *tgt, char *buf)
{
	int i, p, bull, cow, n = strlen(tgt);
 
	for (i = 0, p = 1; i < n && (p *= 9 - i); i++);
	list = malloc(p * (n + 1));
 
	pick(n, 0, 0, buf);
	for (p = 1, bull = 0; n - bull; p++) {
		strcpy(buf, list + (n + 1) * irand(len));
		bull = score(tgt, buf, &cow);
 
		printf("Guess %2d| %s    (from: %d)\n"
			"Score   | %d bull, %d cow\n%s",
			p, buf, len, bull, cow, line);
 
		filter(buf, n, bull, cow);
	}
}
 
int main(int c, char **v)
{
	int n = c > 1 ? atoi(v[1]) : 4;
 
	char secret[10] = "", answer[10] = "";
	srand(time(0));
 
	printf("%sSecret  | %s\n%s", line, get_digits(n, secret), line);
	game(secret, answer);
 
	return 0;
}