【rCore OS 开源操作系统】Rust HashMap应用 知识点及练习题

前言

这一章节中的题目难度一下子就起来了,难度主要在两个方面:

  • Rust 特性 + HashMap 相关 API 不熟悉
  • 题目理解(英语理解能力丧失ed

不知道 HashMap API,问题也不大:

  • rustup doc 启动本地文档查找相关 API。
  • rustlings hint hashmaps 获取提示。

这里的提示是Rust圣经(《The Rust Programming Language》)上的内容:

语法大概就是这么一回事:

use std::collections::HashMap;

let mut scores = HashMap::new();

scores.insert(String::from("Blue"), 10);
scores.insert(String::from("Yellow"), 50);

let team_name = String::from("Blue");
// unwrap_or(0) 的意思是,如果为空,那么返回0
let score = scores.get(&team_name).copied().unwrap_or(0);

其他的 API 也是一样,遇到问题了再查。

练习题

HashMap1

我们需要往一个篮子里面装水果——随便什么都行,只需要满足两个条件:

  • 种类 >= 3
  • 总数 >= 5
题目
// hashmaps1.rs
//
// A basket of fruits in the form of a hash map needs to be defined. The key
// represents the name of the fruit and the value represents how many of that
// particular fruit is in the basket. You have to put at least three different
// types of fruits (e.g apple, banana, mango) in the basket and the total count
// of all the fruits should be at least five.
//
// Make me compile and pass the tests!
//
// Execute `rustlings hint hashmaps1` or use the `hint` watch subcommand for a
// hint.

// I AM NOT DONE

use std::collections::HashMap;

fn fruit_basket() -> HashMap<String, u32> {
    let mut basket = // TODO: declare your hash map here.

    // Two bananas are already given for you :)
    basket.insert(String::from("banana"), 2);

    // TODO: Put more fruits in your basket here.

    basket
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn at_least_three_types_of_fruits() {
        let basket = fruit_basket();
        assert!(basket.len() >= 3);
    }

    #[test]
    fn at_least_five_fruits() {
        let basket = fruit_basket();
        assert!(basket.values().sum::<u32>() >= 5);
    }
}

题解

也就是最基本的应用了。

// hashmaps1.rs
//
// A basket of fruits in the form of a hash map needs to be defined. The key
// represents the name of the fruit and the value represents how many of that
// particular fruit is in the basket. You have to put at least three different
// types of fruits (e.g apple, banana, mango) in the basket and the total count
// of all the fruits should be at least five.
//
// Make me compile and pass the tests!
//
// Execute `rustlings hint hashmaps1` or use the `hint` watch subcommand for a
// hint.

use std::collections::HashMap;

fn fruit_basket() -> HashMap<String, u32> {
    let mut basket = HashMap::new(); // TODO: declare your hash map here.

    // Two bananas are already given for you :)
    basket.insert(String::from("banana"), 2);

    // TODO: Put more fruits in your basket here.
    basket.insert(String::from("apple 🍎"), 1);
    basket.insert(String::from("lemon 🍋"), 666);
    basket
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn at_least_three_types_of_fruits() {
        let basket = fruit_basket();
        assert!(basket.len() >= 3);
    }

    #[test]
    fn at_least_five_fruits() {
        let basket = fruit_basket();
        assert!(basket.values().sum::<u32>() >= 5);
    }
}

HashMap2

题目

这次是需要用 HashMap 统计每种水果数量。

// hashmaps2.rs
//
// We're collecting different fruits to bake a delicious fruit cake. For this,
// we have a basket, which we'll represent in the form of a hash map. The key
// represents the name of each fruit we collect and the value represents how
// many of that particular fruit we have collected. Three types of fruits -
// Apple (4), Mango (2) and Lychee (5) are already in the basket hash map. You
// must add fruit to the basket so that there is at least one of each kind and
// more than 11 in total - we have a lot of mouths to feed. You are not allowed
// to insert any more of these fruits!
//
// Make me pass the tests!
//
// Execute `rustlings hint hashmaps2` or use the `hint` watch subcommand for a
// hint.

// I AM NOT DONE

use std::collections::HashMap;

#[derive(Hash, PartialEq, Eq)]
enum Fruit {
    Apple,
    Banana,
    Mango,
    Lychee,
    Pineapple,
}

fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
    let fruit_kinds = vec![
        Fruit::Apple,
        Fruit::Banana,
        Fruit::Mango,
        Fruit::Lychee,
        Fruit::Pineapple,
    ];

    for fruit in fruit_kinds {
        // TODO: Insert new fruits if they are not already present in the
        // basket. Note that you are not allowed to put any type of fruit that's
        // already present!
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // Don't modify this function!
    fn get_fruit_basket() -> HashMap<Fruit, u32> {
        let mut basket = HashMap::<Fruit, u32>::new();
        basket.insert(Fruit::Apple, 4);
        basket.insert(Fruit::Mango, 2);
        basket.insert(Fruit::Lychee, 5);

        basket
    }

    #[test]
    fn test_given_fruits_are_not_modified() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        assert_eq!(*basket.get(&Fruit::Apple).unwrap(), 4);
        assert_eq!(*basket.get(&Fruit::Mango).unwrap(), 2);
        assert_eq!(*basket.get(&Fruit::Lychee).unwrap(), 5);
    }

    #[test]
    fn at_least_five_types_of_fruits() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        let count_fruit_kinds = basket.len();
        assert!(count_fruit_kinds >= 5);
    }

    #[test]
    fn greater_than_eleven_fruits() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        let count = basket.values().sum::<u32>();
        assert!(count > 11);
    }
    
    #[test]
    fn all_fruit_types_in_basket() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        for amount in basket.values() {
            assert_ne!(amount, &0);
        }
    }
}

题解
// hashmaps2.rs
//
// We're collecting different fruits to bake a delicious fruit cake. For this,
// we have a basket, which we'll represent in the form of a hash map. The key
// represents the name of each fruit we collect and the value represents how
// many of that particular fruit we have collected. Three types of fruits -
// Apple (4), Mango (2) and Lychee (5) are already in the basket hash map. You
// must add fruit to the basket so that there is at least one of each kind and
// more than 11 in total - we have a lot of mouths to feed. You are not allowed
// to insert any more of these fruits!
//
// Make me pass the tests!
//
// Execute `rustlings hint hashmaps2` or use the `hint` watch subcommand for a
// hint.

use std::collections::HashMap;

#[derive(Hash, PartialEq, Eq)]
enum Fruit {
    Apple,
    Banana,
    Mango,
    Lychee,
    Pineapple,
}

fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
    let fruit_kinds = vec![
        Fruit::Apple,
        Fruit::Banana,
        Fruit::Mango,
        Fruit::Lychee,
        Fruit::Pineapple,
    ];

    for fruit in fruit_kinds {
        match basket.get(&fruit) {
            Some(_) => {}
            None => {
                basket.insert(fruit, 1);
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    // Don't modify this function!
    fn get_fruit_basket() -> HashMap<Fruit, u32> {
        let mut basket = HashMap::<Fruit, u32>::new();
        basket.insert(Fruit::Apple, 4);
        basket.insert(Fruit::Mango, 2);
        basket.insert(Fruit::Lychee, 5);

        basket
    }

    #[test]
    fn test_given_fruits_are_not_modified() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        assert_eq!(*basket.get(&Fruit::Apple).unwrap(), 4);
        assert_eq!(*basket.get(&Fruit::Mango).unwrap(), 2);
        assert_eq!(*basket.get(&Fruit::Lychee).unwrap(), 5);
    }

    #[test]
    fn at_least_five_types_of_fruits() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        let count_fruit_kinds = basket.len();
        assert!(count_fruit_kinds >= 5);
    }

    #[test]
    fn greater_than_eleven_fruits() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        let count = basket.values().sum::<u32>();
        assert!(count > 11);
    }

    #[test]
    fn all_fruit_types_in_basket() {
        let mut basket = get_fruit_basket();
        fruit_basket(&mut basket);
        for amount in basket.values() {
            assert_ne!(amount, &0);
        }
    }
}

HashMap3

题目

说来惭愧,这个题目的题意我是读了几遍才大概看懂…

大概意思就是几个队伍进行球赛,需要统计每个队伍的进球数丢球数

其中比较难的点在于,需要用到不太了解的 HashMap 的 entry API,同时涉及到字符串所有权问题,新人上手不太熟悉可能会感到比较迷惑。

// hashmaps3.rs
//
// A list of scores (one per line) of a soccer match is given. Each line is of
// the form : "<team_1_name>,<team_2_name>,<team_1_goals>,<team_2_goals>"
// Example: England,France,4,2 (England scored 4 goals, France 2).
//
// You have to build a scores table containing the name of the team, goals the
// team scored, and goals the team conceded. One approach to build the scores
// table is to use a Hashmap. The solution is partially written to use a
// Hashmap, complete it to pass the test.
//
// Make me pass the tests!
//
// Execute `rustlings hint hashmaps3` or use the `hint` watch subcommand for a
// hint.

// I AM NOT DONE

use std::collections::HashMap;

// A structure to store the goal details of a team.
struct Team {
    goals_scored: u8,
    goals_conceded: u8,
}

fn build_scores_table(results: String) -> HashMap<String, Team> {
    // The name of the team is the key and its associated struct is the value.
    let mut scores: HashMap<String, Team> = HashMap::new();

    for r in results.lines() {
        let v: Vec<&str> = r.split(',').collect();
        let team_1_name = v[0].to_string();
        let team_1_score: u8 = v[2].parse().unwrap();
        let team_2_name = v[1].to_string();
        let team_2_score: u8 = v[3].parse().unwrap();
        // TODO: Populate the scores table with details extracted from the
        // current line. Keep in mind that goals scored by team_1
        // will be the number of goals conceded from team_2, and similarly
        // goals scored by team_2 will be the number of goals conceded by
        // team_1.
    }
    scores
}

#[cfg(test)]
mod tests {
    use super::*;

    fn get_results() -> String {
        let results = "".to_string()
            + "England,France,4,2\n"
            + "France,Italy,3,1\n"
            + "Poland,Spain,2,0\n"
            + "Germany,England,2,1\n";
        results
    }

    #[test]
    fn build_scores() {
        let scores = build_scores_table(get_results());

        let mut keys: Vec<&String> = scores.keys().collect();
        keys.sort();
        assert_eq!(
            keys,
            vec!["England", "France", "Germany", "Italy", "Poland", "Spain"]
        );
    }

    #[test]
    fn validate_team_score_1() {
        let scores = build_scores_table(get_results());
        let team = scores.get("England").unwrap();
        assert_eq!(team.goals_scored, 5);
        assert_eq!(team.goals_conceded, 4);
    }

    #[test]
    fn validate_team_score_2() {
        let scores = build_scores_table(get_results());
        let team = scores.get("Spain").unwrap();
        assert_eq!(team.goals_scored, 0);
        assert_eq!(team.goals_conceded, 2);
    }
}

题解
// hashmaps3.rs
//
// A list of scores (one per line) of a soccer match is given. Each line is of
// the form : "<team_1_name>,<team_2_name>,<team_1_goals>,<team_2_goals>"
// Example: England,France,4,2 (England scored 4 goals, France 2).
//
// You have to build a scores table containing the name of the team, goals the
// team scored, and goals the team conceded. One approach to build the scores
// table is to use a Hashmap. The solution is partially written to use a
// Hashmap, complete it to pass the test.
//
// Make me pass the tests!
//
// Execute `rustlings hint hashmaps3` or use the `hint` watch subcommand for a
// hint.

// use std::collections::hash_map::Entry;
use std::collections::HashMap;

// A structure to store the goal details of a team.
struct Team {
    goals_scored: u8,
    goals_conceded: u8,
}

fn build_scores_table(results: String) -> HashMap<String, Team> {
    // The name of the team is the key and its associated struct is the value.
    let mut scores: HashMap<String, Team> = HashMap::new();

    for r in results.lines() {
        let v: Vec<&str> = r.split(',').collect();
        let team_1_name = v[0].to_string();
        let team_1_score: u8 = v[2].parse().unwrap();
        let team_2_name = v[1].to_string();
        let team_2_score: u8 = v[3].parse().unwrap();
        // TODO: Populate the scores table with details extracted from the
        // current line. Keep in mind that goals scored by team_1
        // will be the number of goals conceded from team_2, and similarly
        // goals scored by team_2 will be the number of goals conceded by
        // team_1.
        // scores.get(team_1_name)
        scores.entry(team_1_name.clone()).or_insert(Team {
            goals_scored: 0,
            goals_conceded: 0,
        });
        let team1_info = scores.get_mut(&team_1_name).unwrap();
        team1_info.goals_scored += team_1_score;
        team1_info.goals_conceded += team_2_score;

        scores.entry(team_2_name.clone()).or_insert(Team {
            goals_scored: 0,
            goals_conceded: 0,
        });
        let team2_info = scores.get_mut(&team_2_name).unwrap();

		// team1_info 的更改不能放到最后,这样会有所有权转移问题
		// team1_info.goals_scored += team_1_score;
        // team1_info.goals_conceded += team_2_score;
        team2_info.goals_scored += team_2_score;
        team2_info.goals_conceded += team_1_score;
    }
    scores
}

#[cfg(test)]
mod tests {
    use super::*;

    fn get_results() -> String {
        let results = "".to_string()
            + "England,France,4,2\n"
            + "France,Italy,3,1\n"
            + "Poland,Spain,2,0\n"
            + "Germany,England,2,1\n";
        results
    }

    #[test]
    fn build_scores() {
        let scores = build_scores_table(get_results());

        let mut keys: Vec<&String> = scores.keys().collect();
        keys.sort();
        assert_eq!(
            keys,
            vec!["England", "France", "Germany", "Italy", "Poland", "Spain"]
        );
    }

    #[test]
    fn validate_team_score_1() {
        let scores = build_scores_table(get_results());
        let team = scores.get("England").unwrap();
        assert_eq!(team.goals_scored, 5);
        assert_eq!(team.goals_conceded, 4);
    }

    #[test]
    fn validate_team_score_2() {
        let scores = build_scores_table(get_results());
        let team = scores.get("Spain").unwrap();
        assert_eq!(team.goals_scored, 0);
        assert_eq!(team.goals_conceded, 2);
    }
}

10-05 02:00