#147683 (Rust) No.4 おもりと天秤

• 問題: No.4 おもりと天秤
• ユーザー: tsubu_taiyaki
• 提出日時: 2017-02-04 07:33:53
• 言語: Rust (1.94.0 + proconio + num + itertools)
• 結果: CE (最新)
  AC
  (最初)
• 実行時間: -
• コード長: 1,573 bytes
• コンパイル時間: 396 ms
• コンパイル使用メモリ: 138,288 KB
• 最終ジャッジ日時: 2026-05-10 04:35:36
• 合計ジャッジ時間: 3,002 ms
• ジャッジサーバーID （参考情報）: judge1_1 / judge2_0

コンパイルメッセージ

error[E0782]: expected a type, found a trait
 --> src/main.rs:9:21
  |
9 |     tokens: &'a mut Iterator<Item = String>,
  |                     ^^^^^^^^^^^^^^^^^^^^^^^
  |
help: you can add the `dyn` keyword if you want a trait object
  |
9 |     tokens: &'a mut dyn Iterator<Item = String>,
  |                     +++

error[E0782]: expected a type, found a trait
  --> src/main.rs:13:23
   |
13 |     fn new(i: &'a mut Iterator<Item = String>) -> Self {
   |                       ^^^^^^^^^^^^^^^^^^^^^^^
   |
help: use a new generic type parameter, constrained by `Iterator<Item = String>`
   |
13 -     fn new(i: &'a mut Iterator<Item = String>) -> Self {
13 +     fn new<T: Iterator<Item = String>>(i: &'a mut T) -> Self {
   |
help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
   |
13 |     fn new(i: &'a mut impl Iterator<Item = String>) -> Self {
   |                       ++++
help: alternatively, use a trait object to accept any type that implements `Iterator<Item = String>`, accessing its methods at runtime using dynamic dispatch
   |
13 |     fn new(i: &'a mut dyn Iterator<Item = String>) -> Self {
   |                       +++

error[E0282]: type annotations needed
  --> src/main.rs:24:34
   |
24 |         self.tokens.take(n).map(|s| match s.parse() { Ok(x) => x, Err(_) => panic!() } ).collect()
   |                                  ^        - type must be known at this point
   |
help: consider giving this closure parameter an explicit type
   |
24 |         self.tokens.take(n).map(|s: /* Type */| match s.parse() { Ok(x) => x, Err(_) => panic!() } ).collect()
   |                                   ++++++++++++

Some errors have detailed explanations: E0282, E0782.
For more information about an error, try `rustc --explain E0282`.
error: could not compile `main` (bin "main") due to 3 previous errors

ソースコード

#![allow(unused_imports)]

use std::io::{self, BufRead};
use std::str::FromStr;
use std::collections::*;
use std::cmp::*;

struct Parser<'a> {
    tokens: &'a mut Iterator<Item = String>,
}

impl<'a> Parser<'a> {
    fn new(i: &'a mut Iterator<Item = String>) -> Self {
        Parser {tokens: i}
    }
    fn take<T: FromStr>(&mut self) -> T {
        match self.tokens.next().expect("empty iterator").parse() {
            Ok(x) => x,
            Err(_) => panic!()
        }
    }

    fn take_some<T: FromStr>(&mut self, n: usize) -> Vec<T> {
        self.tokens.take(n).map(|s| match s.parse() { Ok(x) => x, Err(_) => panic!() } ).collect()
    }
}

fn main() {
    let stdin = io::stdin();
    let mut tokens = stdin.lock().lines().filter_map(|x| x.ok()).flat_map(|x| x.split_whitespace().map(|s| s.to_owned()).collect::<Vec<String>>());
    let mut parser = Parser::new(&mut tokens);

    let n: i64 = parser.take();
    let w: Vec<i64> = parser.take_some(n as usize);

    let s: i64 = w.iter().sum();
    if s % 2 == 1 {
        println!("impossible");
        return;
    }
    let mut dp = Vec::new();
    dp.push(Vec::new());
    dp[0].resize(s as usize, false);
    dp[0][0] = true;
    for i in 0..n {
        let mut v = Vec::new();
        {
            let last = &dp[i as usize];
            for j in 0..s {
                v.push(last[j as usize] || (j - w[i as usize] >= 0 && last[(j-w[i as usize]) as usize]));
            }
        }
        dp.push(v);
    }
    println!("{}", if dp[n as usize][(s/2) as usize] {"possible"} else {"impossible"});
}