Slashdot Mirror
A Rock Paper Scissors Brainteaser
New submitter arsheive (609065) writes with a link to this interesting RPS brainteaser: "How do you play against an opponent who _must_ throw Rock 50% of the time, and how much would you be willing to pay to play against them?"
Sorry, but Slashdot mangled that code badly because of the angle brackets.
Let me try again:
#include <stdio.h>
struct rps {
double rock;
double paper;
double scissors;
};
static double
eval(struct rps *a, struct rps *b)
{
return
(a->rock * (b->scissors - b->paper)) +
(a->paper * (b->rock - b->scissors)) +
(a->scissors * (b->paper - b->rock));
}
int
main(void)
{
struct rps you;
struct rps him;
him.rock = 0.5;
double worst_best_eval_for_him = 1.0;
double best_rock_for_you = 0;
double best_paper_for_you = 0;
double worst_best_paper_for_him = 0;
double dx = 0.001;
for (you.rock = 0; you.rock < 1.0; you.rock += dx) {
for (you.paper= 0; (you.paper + you.rock) < 1.0; you.paper+= dx) {
you.scissors = 1.0 - you.rock - you.paper;
double best_paper_for_him = 0.0;
double best_eval_for_him = -1.0;
for (him.paper = 0; him.paper < 0.5; him.paper += dx) {
him.scissors = 1.0 - him.rock - him.paper;
double p = eval(&him, &you);
if (p > best_eval_for_him) {
best_eval_for_him = p;
best_paper_for_him = him.paper;
}
}
if (worst_best_eval_for_him > best_eval_for_him) {
worst_best_eval_for_him = best_eval_for_him;
best_rock_for_you = you.rock;
best_paper_for_you = you.paper;
worst_best_paper_for_him = best_paper_for_him;
}
}
}
printf("worst_best_eval_for_him = %f\n", worst_best_eval_for_him);
printf("best_rock_for_you = %f\n", best_rock_for_you);
printf("best_paper_for_you = %f\n", best_paper_for_you);
printf("worst_best_paper_for_him = %f\n", worst_best_paper_for_him);
return 0;
}