モンテカルロ法で三目並べの勝率計算

tic_tac_toe.rs

extern crate rand;
use rand::{thread_rng, Rng};

fn end(board: &Vec<i32>) -> usize {
    // 縦
    for i in 0..3 {
        let mut sum = 0;
        for j in 0..3 {
            sum = sum + board[i * 3 + j];
        }
        if sum == 3 {
            return 0;
        } else if sum == -3 {
            return 1;
        }
    }
    for j in 0..3 {
        let mut sum = 0;
        for i in 0..3 {
            sum = sum + board[i * 3 + j];
        }
        if sum == 3 {
            return 0;
        } else if sum == -3 {
            return 1;
        }
    }
    let mut sum = 0;
    for i in 0..3 {
        sum = sum + board[i * 3 + i];
    }
    if sum == 3 {
        return 0;
    } else if sum == -3 {
        return 1;
    }
    let mut sum = 0;
    for i in 0..3 {
        sum = sum + board[i * 3 + (2 - i)];
    }
    if sum == 3 {
        return 0;
    } else if sum == -3 {
        return 1;
    }
    2
}

fn check(v: &Vec<usize>) -> usize {
    let mut board: Vec<i32> = vec![0; 9];
    let mut c = 1;
    for i in v {
        board[*i] = c;
        c = -c;
        let idx = end(&board);
        if idx < 2 {
            return idx;
        }
    }
    end(&board)
}

fn main() {
    let mut v: Vec<usize> = (0..9).collect();
    let mut count = vec![0; 3];

    let mut rng = thread_rng();
    let n = 10000000;

    for _ in 0..n {
        rng.shuffle(&mut v);
        let idx = check(&v);
        count[idx] = count[idx] + 1;
    }
    println!("{:?}", count);
    let se: Vec<f64> = count
        .iter()
        .map(|c| {
            let p = (*c as f64) / (n as f64);
            (p * (1.0 - p) / (n as f64)).sqrt()
        })
        .collect();
    println!("{:?}", se);
}