solutions

exercises/src/bin/exercise_01.rs

@@ -4,7 +4,7 @@
 ///
 
 fn exercise() -> i32 {
-    let output = 7;
+    let mut output = 7;
 
     // Do not change below this line __________________________________________
     println!("The value of output is: {}", output);

exercises/src/bin/exercise_02.rs

@@ -7,7 +7,7 @@ fn exercise() -> i32 {
     let output = 7; // Do not change this line
 
     println!("The value of output is: {}", output);
-    output = 5;
+    let output = 5;
     println!("The value of output is: {}", output);
     output // Do not change this line
 }

exercises/src/bin/exercise_03.rs

@@ -9,7 +9,7 @@ fn exercise() -> i32 {
     let mut output = "seven"; // Do not change this line
 
     println!("The value of output is: {}", output);
-    output = 5;
+    let output = 5;
     println!("The value of output is: {}", output);
     output // Do not change this line
 }

exercises/src/bin/exercise_04.rs

@@ -9,7 +9,7 @@ fn exercise() -> i32 {
     let mut output = 7; // Do not change this line
     {
         println!("The value of output is: {}", output);
-        output = 5; // <-- how to tell the compiler that this is a different variable?
+        let output = 5; // <-- how to tell the compiler that this is a different variable?
         println!("The value of output is: {}", output);
     }
     output // Do not change this line

exercises/src/bin/exercise_05.rs

@@ -10,7 +10,7 @@ fn exercise() -> i32 {
 }
 
 fn square(value: i32) -> i32 {
-    value * value;
+    value * value
 }
 
 fn main() {

exercises/src/bin/exercise_06.rs

@@ -9,12 +9,13 @@ fn exercise() -> i32 {
     divide(value)
 }
 
-fn divide(value: i32) {
+#[allow(clippy::eq_op)]
+fn divide(value: i32) -> i32 {
     if value == 0 {
         0
     } else {
         value / value
-    };
+    }
 }
 
 fn main() {

exercises/src/bin/exercise_07.rs

@@ -12,10 +12,12 @@ fn exercise() -> String {
     let c = String::from("five");
     let d = c;
 
-    // format!("{a}={c}")
-    // format!("{b}={c}")
-    // format!("{a}={d}")
-    // format!("{b}={d}")
+    // format!("{a}={c}") // Invalid: borrow of moved value `c`
+    // format!("{b}={c}") // Invalid: borrow of moved value `c`
+    format!("{a}={d}") // Valid: as a is a primitive type, it has a copy trait,
+                       // meaning that b is not taking ownership but is a copy of a
+                       // format!("{b}={d}") // Valid: as a is a primitive type, it has a copy trait,
+                       // meaning that b is not taking ownership but is a copy of a
 }
 
 fn main() {

exercises/src/bin/exercise_08.rs

@@ -7,7 +7,7 @@
 #[allow(unused)]
 fn exercise() -> String {
     let value = String::from("Hello world");
-    read_string(value);
+    let value = read_string(value);
     value
 }
 

exercises/src/bin/exercise_09.rs

@@ -9,12 +9,12 @@
 fn exercise() -> String {
     // Do not change this function
     let value = String::from("Hello world");
-    read_string(value);
-    read_string(value);
+    read_string(&value);
+    read_string(&value);
     value
 }
 
-fn read_string(value: String) {
+fn read_string(value: &String) {
     println!("{}", value);
 }
 

exercises/src/bin/exercise_10.rs

@@ -11,7 +11,7 @@ fn exercise() -> String {
     value
 }
 
-fn read_first_word() {
+fn read_first_word(value: &str) -> &str {
     // Adjust the signature of this function to make the example compile
     value.split_once(' ').unwrap().0
 }

exercises/src/bin/exercise_11.rs

@@ -5,12 +5,12 @@
 /// value by 2? Hint: refer to exercise_01 to see how to add mutability to a variable.
 ///
 fn exercise() -> i32 {
-    let value = 5;
-    times_two(value);
+    let mut value = 5;
+    times_two(&mut value);
     value
 }
 
-fn times_two(value: i32) {
+fn times_two(value: &mut i32) {
     *value *= 2; // This line does not require any changes!
 }
 

exercises/src/bin/exercise_12.rs

@@ -6,7 +6,7 @@
 fn exercise() -> i32 {
     let tuple = (1, 2, 3, 5, 13, 21, 34);
 
-    todo!("return the correct entry from the tuple")
+    tuple.3
 }
 
 fn main() {

exercises/src/bin/exercise_13.rs

@@ -6,7 +6,8 @@
 ///
 
 fn exercise() -> (i32, String) {
-    todo!("Call get_input and return the sum of all i32 and the concatenation of all Strings")
+    let (a, b, c, d, e) = get_input();
+    (a + c + e, format!("{}{}", b, d))
 }
 
 fn get_input() -> (i32, String, i32, String, i32) {

exercises/src/bin/exercise_14.rs

@@ -18,6 +18,11 @@ struct Order {
     shipping: i32,
     tax: i32,
 }
+impl Order {
+    fn total_cost(&self) -> i32 {
+        self.cost + self.shipping + self.tax
+    }
+}
 
 fn main() {
     exercise();

exercises/src/bin/exercise_15.rs

@@ -26,6 +26,11 @@ struct Order {
     shipping: i32,
     tax: i32,
 }
+impl Order {
+    fn apply_discount_to_cost(&mut self, discount: i32) {
+        self.cost -= discount;
+    }
+}
 
 fn main() {
     exercise();

exercises/src/bin/exercise_16.rs

@@ -32,6 +32,10 @@ impl Order {
     fn cost_without_tax(&self) -> i32 {
         self.cost + self.shipping
     }
+
+    fn have_equal_cost_without_tax(order1: &Order, order2: &Order) -> bool {
+        order1.cost_without_tax() == order2.cost_without_tax()
+    }
 }
 
 fn main() {

exercises/src/bin/exercise_17.rs

@@ -12,7 +12,8 @@ fn exercise() -> i32 {
     let shipping = 10;
     let tax = 5;
 
-    todo!("Create an order using the builder pattern");
+    let order = OrderBuilder::new(cost).shipping(shipping).tax(tax).build();
+    order.total_cost()
 }
 
 #[allow(unused)]

exercises/src/bin/exercise_18.rs

@@ -4,7 +4,7 @@
 /// is positive, -1 if the number is negative, and 0 if the number is zero.
 ///
 
-fn exercise() -> () {
+fn exercise() {
     // Do not change this function
     println!("Sign for 5 is {}", sign(5));
     println!("Sign for 25 is {}", sign(25));
@@ -13,7 +13,13 @@ fn exercise() -> () {
 }
 
 fn sign(value: i32) -> i32 {
-    todo!("implement sign function here")
+    if value > 0 {
+        1
+    } else if value < 0 {
+        -1
+    } else {
+        0
+    }
 }
 
 fn main() {

exercises/src/bin/exercise_19.rs

@@ -6,7 +6,9 @@
 fn exercise() -> i32 {
     let mut sum = 0;
 
-    todo!("Sum the numbers from 1 to 100 and store the result in the variable `sum` here");
+    for i in 1..=100 {
+        sum += i;
+    }
 
     sum
 }

exercises/src/bin/exercise_20.rs

@@ -17,6 +17,19 @@ enum TrafficLight {
     Yellow,
     Green,
 }
+impl TrafficLight {
+    fn switch_to_next(&self) -> TrafficLight {
+        if self == &TrafficLight::Green {
+            TrafficLight::Yellow
+        } else if self == &TrafficLight::Yellow {
+            TrafficLight::Red
+        } else if self == &TrafficLight::Red {
+            TrafficLight::Green
+        } else {
+            unreachable!()
+        }
+    }
+}
 
 fn main() {
     exercise();

exercises/src/bin/exercise_21.rs

@@ -4,7 +4,7 @@
 /// Try to use pattern matching to implement the method.
 ///
 
-fn exercise() -> () {
+fn exercise() {
     // Do not change this function
     println!("Dog sound: {}", Animal::Dog.make_sound());
     println!("Cat sound: {}", Animal::Cat.make_sound());
@@ -17,6 +17,15 @@ enum Animal {
     Cat,
     Cow,
 }
+impl Animal {
+    fn make_sound(&self) -> &str {
+        match self {
+            Animal::Dog => "Woof",
+            Animal::Cat => "Meow",
+            Animal::Cow => "Moo",
+        }
+    }
+}
 
 fn main() {
     exercise();

exercises/src/bin/exercise_22.rs

@@ -8,8 +8,9 @@ fn exercise() -> i32 {
     let mut sum = 0;
 
     for i in 1..=100 {
-        let divided = integer_divided_by_two(i);
-        todo!("If the `integer_divided_by_two` function returns Some value, add its output to the sum");
+        if let Some(value) = integer_divided_by_two(i) {
+            sum += value;
+        }
     }
 
     sum

exercises/src/bin/exercise_23.rs

@@ -6,7 +6,11 @@
 use std::num::ParseIntError;
 
 fn exercise(input: &str) -> i32 {
-    todo!();
+    if let Ok(value) = int_value(input) {
+        value
+    } else {
+        0
+    }
 }
 
 #[allow(dead_code)]

exercises/src/bin/exercise_24.rs

@@ -23,6 +23,17 @@ struct Square {
 struct Circle {
     value: f32,
 }
+impl Area for Square {
+    fn area(&self) -> f32 {
+        self.value * self.value
+    }
+}
+impl Area for Circle {
+    fn area(&self) -> f32 {
+        let radius = self.value / 2.0;
+        core::f32::consts::PI * radius * radius
+    }
+}
 
 trait Area {
     fn area(&self) -> f32;

exercises/src/bin/exercise_25.rs

@@ -21,6 +21,10 @@ fn exercise() -> String {
     )
 }
 
+fn get_first<T>(pair: (T, T)) -> T {
+    pair.0
+}
+
 fn main() {
     println!("{}", exercise());
 }

exercises/src/bin/exercise_26.rs

@@ -8,19 +8,29 @@ use std::collections::{HashMap, HashSet};
 
 fn vector_sum(vector: Vec<i32>) -> i32 {
     let mut total = 0;
-    todo!("Return the sum of the vector");
+    for i in vector {
+        total += i;
+    }
     total
 }
 
 fn hashset_product(hashset: HashSet<i32>) -> i32 {
     let mut total = 1;
-    todo!("Return the product of the hashset");
+    for i in hashset {
+        total *= i;
+    }
     total
 }
 
 fn hashmap_sum(hashmap: HashMap<&str, Vec<i32>>) -> HashMap<&str, i32> {
     let mut total = HashMap::new();
-    todo!("Return the sum of the hashmap values per key");
+    for (key, value) in hashmap {
+        let mut sum = 0;
+        for i in value {
+            sum += i;
+        }
+        total.insert(key, sum);
+    }
     total
 }
 

exercises/src/bin/exercise_27.rs

@@ -6,7 +6,8 @@
 ///
 
 fn exercise(a: i32, b: i32) -> i32 {
-    todo!("Call the apply function twice with a closure defined above");
+    let sum = apply(|a, b| a + b, a, b);
+    apply(|a, b| a * b, sum, b)
 }
 
 fn apply<F: Fn(i32, i32) -> i32>(func: F, a: i32, b: i32) -> i32 {

exercises/src/bin/exercise_28.rs

@@ -7,15 +7,18 @@ use std::collections::{HashMap, HashSet};
 ///
 
 fn vector_sum(vector: Vec<i32>) -> i32 {
-    todo!("Return the sum of the vector");
+    vector.into_iter().sum()
 }
 
 fn hashset_product(hashset: HashSet<i32>) -> i32 {
-    todo!("Return the product of the hashset");
+    hashset.into_iter().product()
 }
 
 fn hashmap_sum(hashmap: HashMap<&str, Vec<i32>>) -> HashMap<&str, i32> {
-    todo!("Return the sum of the hashmap values per key");
+    hashmap
+        .into_iter()
+        .map(|(key, value)| (key, value.into_iter().sum()))
+        .collect()
 }
 
 fn main() {