Update Exercises Directory Names to Reflect Order

exercises/09_strings/README.md

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+# Strings
+
+Rust has two string types, a string slice (`&str`) and an owned string (`String`).
+We're not going to dictate when you should use which one, but we'll show you how
+to identify and create them, as well as use them.
+
+## Further information
+
+- [Strings](https://doc.rust-lang.org/book/ch08-02-strings.html)

exercises/09_strings/strings1.rs

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+// strings1.rs
+//
+// Make me compile without changing the function signature!
+//
+// Execute `rustlings hint strings1` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+fn main() {
+    let answer = current_favorite_color();
+    println!("My current favorite color is {}", answer);
+}
+
+fn current_favorite_color() -> String {
+    "blue"
+}

exercises/09_strings/strings2.rs

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+// strings2.rs
+//
+// Make me compile without changing the function signature!
+//
+// Execute `rustlings hint strings2` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+fn main() {
+    let word = String::from("green"); // Try not changing this line :)
+    if is_a_color_word(word) {
+        println!("That is a color word I know!");
+    } else {
+        println!("That is not a color word I know.");
+    }
+}
+
+fn is_a_color_word(attempt: &str) -> bool {
+    attempt == "green" || attempt == "blue" || attempt == "red"
+}

exercises/09_strings/strings3.rs

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+// strings3.rs
+//
+// Execute `rustlings hint strings3` or use the `hint` watch subcommand for a
+// hint.
+
+// I AM NOT DONE
+
+fn trim_me(input: &str) -> String {
+    // TODO: Remove whitespace from both ends of a string!
+    ???
+}
+
+fn compose_me(input: &str) -> String {
+    // TODO: Add " world!" to the string! There's multiple ways to do this!
+    ???
+}
+
+fn replace_me(input: &str) -> String {
+    // TODO: Replace "cars" in the string with "balloons"!
+    ???
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn trim_a_string() {
+        assert_eq!(trim_me("Hello!     "), "Hello!");
+        assert_eq!(trim_me("  What's up!"), "What's up!");
+        assert_eq!(trim_me("   Hola!  "), "Hola!");
+    }
+
+    #[test]
+    fn compose_a_string() {
+        assert_eq!(compose_me("Hello"), "Hello world!");
+        assert_eq!(compose_me("Goodbye"), "Goodbye world!");
+    }
+
+    #[test]
+    fn replace_a_string() {
+        assert_eq!(replace_me("I think cars are cool"), "I think balloons are cool");
+        assert_eq!(replace_me("I love to look at cars"), "I love to look at balloons");
+    }
+}

exercises/09_strings/strings4.rs

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+// strings4.rs
+//
+// Ok, here are a bunch of values-- some are `String`s, some are `&str`s. Your
+// task is to call one of these two functions on each value depending on what
+// you think each value is. That is, add either `string_slice` or `string`
+// before the parentheses on each line. If you're right, it will compile!
+//
+// No hints this time!
+
+// I AM NOT DONE
+
+fn string_slice(arg: &str) {
+    println!("{}", arg);
+}
+fn string(arg: String) {
+    println!("{}", arg);
+}
+
+fn main() {
+    ???("blue");
+    ???("red".to_string());
+    ???(String::from("hi"));
+    ???("rust is fun!".to_owned());
+    ???("nice weather".into());
+    ???(format!("Interpolation {}", "Station"));
+    ???(&String::from("abc")[0..1]);
+    ???("  hello there ".trim());
+    ???("Happy Monday!".to_string().replace("Mon", "Tues"));
+    ???("mY sHiFt KeY iS sTiCkY".to_lowercase());
+}