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

Rust_HashMap__0">【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：

点这里可以自己查看：Rust圣经 HashMap语法《The Rust Programming Language》

语法大概就是这么一回事：

rust">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

rust">// 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 DONEuse 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。

rust">// 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。

rust">// 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 DONEuse 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

rust">// 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和丢球数

不懂球，我这里说的“失球数”，就是被对手进球的数量。

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

rust">// 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 DONEuse 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

rust">// 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);}
}