Add hashmaps

hashmap/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "hashmap"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]

hashmap/src/main.rs

@@ -0,0 +1,42 @@
+use std::collections::HashMap;
+
+fn main() {
+    // Create & Insert Into New Hashmap
+    let mut scores = HashMap::new();
+    scores.insert(String::from("Blue"), 10);
+    scores.insert(String::from("Yellow"), 50);
+
+    // Demonstrate Ownership
+    let field_name = String::from("Favorite color");
+    let field_value = 2;
+    scores.insert(field_name, field_value);
+    // field_name and field_value are now owned by hashmap scores
+
+    // Retrieve Value From Hashmap
+    let option = scores.get(String::from("Favourite color").as_str());
+
+    // Iterate Through Hashmap
+    for (key, value) in &scores {
+        println!("[{}] -> {}", key, value);
+    }
+
+    // Overwrite a Value
+    scores.insert(String::from("Blue"), 20);
+    println!("{:?}", scores);
+
+    // Only Insert A Value if Key Has No Value
+    let mut scores2 = HashMap::new();
+    scores2.insert(String::from("Blue"), 10);
+    scores2.entry(String::from("Yellow")).or_insert(50);
+    scores2.entry(String::from("Blue")).or_insert(50);
+    println!("{:?}", scores2);
+
+    // Update Value Based On Pre-existing value
+    let text = "hello world wonderful world";
+    let mut map = HashMap::new();
+    for word in text.split_whitespace() {
+        let count = map.entry(word).or_insert(0);
+        *count += 1;
+    }
+    println!("{:?}", map);
+}