Task: Penney's game
C: #include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define SEQLEN 3

int getseq(char *s)
{
    int r = 0;
    int i = 1 << (SEQLEN - 1);

    while (*s && i) {
        switch (*s++) {
            case 'H':
            case 'h':
                r |= i;
                break;
            case 'T':
            case 't':
                
                break;
            default:
                return -1;
        }
        i >>= 1;
    }

    return r;
}

void printseq(int seq)
{
    int i;
    for (i = SEQLEN - 1; i >= 0; --i)
        printf("%c", seq & (1 << i) ? 'h' : 't');
}

int getuser(void)
{
    int user;
    char s[SEQLEN + 1];

    printf("Enter your sequence of %d (h/t): ", SEQLEN);
    while (1) {
        
        if (scanf("%3s", s) != 1) exit(1);
        if ((user = getseq(s)) != -1) return user;
        printf("Please enter only h/t characters: ");
    }
}

int getai(int user)
{
    int ai;

    printf("Computers sequence of %d is: ", SEQLEN);
    
    if (user == -1)
        ai = rand() & (1 << SEQLEN) - 1;
    else
        ai = (user >> 1) | ((~user << 1) & (1 << SEQLEN - 1));

    printseq(ai);
    printf("\n");
    return ai;
}

int rungame(int user, int ai)
{
    
    int last3 = rand() & (1 << SEQLEN) - 1;

    printf("Tossed sequence: ");
    printseq(last3);
    while (1) {
        if (user == last3) {
            printf("\nUser wins!\n");
            return 1;
        }

        if (ai == last3) {
            printf("\nAi wins!\n");
            return 0;
        }

        last3 = ((last3 << 1) & (1 << SEQLEN) - 2) | (rand() & 1);
        printf("%c", last3 & 1 ? 'h' : 't');
    }
}

int main(void)
{
    srand(time(NULL));
    int playerwins = 0;
    int totalgames = 0;

    
    while (1) {
        int user = -1;
        int ai   = -1;

        printf("\n");
        if (rand() & 1) {
            ai   = getai(user);
            user = getuser();
        }
        else {
            user = getuser();
            ai   = getai(user);
        }
        
        playerwins += rungame(user, ai);
        totalgames++;

        printf("You have won %d out of %d games\n", playerwins, totalgames);
        printf("=================================\n");
    }

    return 0;
}

Java: import java.util.*;

public class PenneysGame {

    public static void main(String[] args) {
        Random rand = new Random();

        String compChoice = "", playerChoice;
        if (rand.nextBoolean()) {

            for (int i = 0; i < 3; i++)
                compChoice += "HT".charAt(rand.nextInt(2));
            System.out.printf("Computer chooses %s%n", compChoice);

            playerChoice = prompt(compChoice);

        } else {

            playerChoice = prompt(compChoice);

            compChoice = "T";
            if (playerChoice.charAt(1) == 'T')
                compChoice = "H";
            compChoice += playerChoice.substring(0, 2);
            System.out.printf("Computer chooses %s%n", compChoice);
        }

        String tossed = "";
        while (true) {
            tossed += "HT".charAt(rand.nextInt(2));
            System.out.printf("Tossed %s%n" , tossed);
            if (tossed.endsWith(playerChoice)) {
                System.out.println("You win!");
                break;
            }
            if (tossed.endsWith(compChoice)) {
                System.out.println("Computer wins!");
                break;
            }
        }
    }

    private static String prompt(String otherChoice) {
        Scanner sc = new Scanner(System.in);
        String s;
        do {
            System.out.print("Choose a sequence: ");
            s = sc.nextLine().trim().toUpperCase();
        } while (!s.matches("[HT]{3}") || s.equals(otherChoice));
        return s;
    }
}