struct Solution;
impl Solution {
    // return type: all situation, not crash situation
    pub fn new21_game(n: i32, k: i32, max_pts: i32) -> f64 {
        let mut mem = vec![0f64; (k + max_pts + 1) as usize];
        for i in k .. k + max_pts + 1 {
            mem[i as usize] = if i <= n { 1f64 } else { 0f64 };
        }
        let mut temp_ans = 0f64;
        if(k - 1 >= 0)
        {
            let i = k - 1;
            for j in 1..max_pts + 1 {
                temp_ans += mem[(i + j) as usize];
            }
            mem[i as usize] = temp_ans as f64 / max_pts as f64;
        }
        for i in (0..k - 1).rev() {
            temp_ans += mem[(i + 1) as usize] - mem[(i + max_pts + 1) as usize];
            mem[i as usize] = temp_ans as f64 / max_pts as f64;
        }
        mem[0]
    }
}

fn main() {
    let sl = Solution::new21_game(21, 17, 10);
    println!("{:?}", sl);
}