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hashmap2: exercises/hashmaps/hashmaps2.rs
题目
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 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);
}
}
}
我们正在收集不同的水果来烘烤美味的水果蛋糕。 为此,我们有一个篮子,我们将以HashMap的形式表示。 key是我们收集的每种水果的名称,value是我们收集的特定水果的数量。 三种水果:Apple苹果(4)、Mango芒果(2)和Lychee荔枝(5)已经在篮子中。 您必须将水果添加到篮子中,以便每种水果至少有一个,总共超过 11 个 !
修改代码让编译顺利通过。
题目解析
先看fruit_basket
函数的注释,要求如果篮子里还没有新水果,请插入新水果。请注意,您不能放入任何已经存在的水果。所以我们只需要放入还没有的水果就可以了:
rust
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!
if !basket.contains_key(&fruit) {
basket.insert(fruit, 1);
}
}
}
也可以使用entry
和or_insert
来插入:
rust
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!
basket.entry(fruit).or_insert(1);
}
}