11 Hash map ~ Python dict. See README.md

exercises/11_hashmaps/README.md

@@ -1,12 +1,49 @@
 # Hashmaps
 
-A *hash map* allows you to associate a value with a particular key.
-You may also know this by the names [*unordered map* in C++](https://en.cppreference.com/w/cpp/container/unordered_map),
-[*dictionary* in Python](https://docs.python.org/3/tutorial/datastructures.html#dictionaries) or an *associative array* in other languages.
+A _hash map_ allows you to associate a value with a particular key.
+You may also know this by the names [_unordered map_ in C++](https://en.cppreference.com/w/cpp/container/unordered_map),
+[_dictionary_ in Python](https://docs.python.org/3/tutorial/datastructures.html#dictionaries) or an _associative array_ in other languages.
 
 This is the other data structure that we've been talking about before, when
 talking about Vecs.
 
+## Syntax
+
+Create, insert values into a hash map, and get a value from a hash map:
+
+```rust
+use std::collections::HashMap;
+
+fn main() {
+    let mut scores = HashMap::new();
+
+    scores.insert(String::from("Blue"), 10);
+    scores.insert(String::from("Yellow"), 50);
+
+    let team_name = String::from("Blue");
+    let score = scores.get(&team_name);
+
+    println!("{:?}", score);
+}
+```
+
+Update a value in a hash map:
+
+```rust
+use std::collections::HashMap;
+
+fn main() {
+    let mut scores = HashMap::new();
+
+    scores.insert(String::from("Blue"), 10);
+
+    // Add 10 to the value of the key "Blue"; or insert the key with a value of 10 if it doesn't exist
+    scores.entry(String::from("Blue")).and_modify(|v| *v += 10).or_insert(10);
+
+    println!("{:?}", scores);
+}
+```
+
 ## Further information
 
 - [Storing Keys with Associated Values in Hash Maps](https://doc.rust-lang.org/book/ch08-03-hash-maps.html)

exercises/11_hashmaps/hashmaps1.rs

@@ -11,17 +11,19 @@
 // Execute `rustlings hint hashmaps1` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
+// https://doc.rust-lang.org/book/ch08-03-hash-maps.html#creating-a-new-hash-map
 
 use std::collections::HashMap;
 
 fn fruit_basket() -> HashMap<String, u32> {
-    let mut basket = // TODO: declare your hash map here.
+    let mut basket = HashMap::new();
 
     // Two bananas are already given for you :)
     basket.insert(String::from("banana"), 2);
 
-    // TODO: Put more fruits in your basket here.
+    // Add at least three different types of fruits
+    basket.insert(String::from("apple"), 1);
+    basket.insert(String::from("mango"), 2);
 
     basket
 }

exercises/11_hashmaps/hashmaps2.rs

@@ -14,7 +14,7 @@
 // Execute `rustlings hint hashmaps2` or use the `hint` watch subcommand for a
 // hint.
 
-// I AM NOT DONE
+// https://doc.rust-lang.org/book/ch08-03-hash-maps.html#adding-a-key-and-value-only-if-a-key-isnt-present
 
 use std::collections::HashMap;
 
@@ -37,9 +37,17 @@ fn fruit_basket(basket: &mut HashMap<Fruit, u32>) {
     ];
 
     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!
+        // 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!
+        // Method 1
+        /*
+        if !basket.contains_key(&fruit) {
+            basket.insert(fruit, 1);
+        }
+         */
+        // Method 2
+        basket.entry(fruit).or_insert(1);
+
     }
 }
 

exercises/11_hashmaps/hashmaps3.rs

@@ -5,17 +5,17 @@
 // Example: England,France,4,2 (England scored 4 goals, France 2).
 //
 // You have to build a scores table containing the name of the team, the total
-// number of goals the team scored, and the total number of 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, 
+// number of goals the team scored, and the total number of 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
+// https://doc.rust-lang.org/book/ch08-03-hash-maps.html#updating-a-value-based-on-the-old-value
 
 use std::collections::HashMap;
 
@@ -35,12 +35,36 @@ fn build_scores_table(results: String) -> HashMap<String, Team> {
         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
+        // 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 by team_2, and similarly
         // goals scored by team_2 will be the number of goals conceded by
         // team_1.
+        // If scores table does not contain the team, insert a new entry and scores. Otherwise, update the scores.
+        scores
+            .entry(team_1_name.clone())
+            .and_modify(|e| {
+                e.goals_scored += team_1_score;
+                e.goals_conceded += team_2_score;
+            })
+            .or_insert(Team {
+                goals_scored: team_1_score,
+                goals_conceded: team_2_score,
+            });
+
+        // Update the scores for team 2
+        scores
+            .entry(team_2_name.clone())
+            .and_modify(|e| {
+                e.goals_scored += team_2_score;
+                e.goals_conceded += team_1_score;
+            })
+            .or_insert(Team {
+                goals_scored: team_2_score,
+                goals_conceded: team_1_score,
+            });
     }
+
     scores
 }