Add solution for sheet2

aufgaben/sheet2/sol1/prime.rs

@@ -0,0 +1,62 @@
+//! Aufgabe 1.2: Primzahltest
+
+fn main() {
+    for i in 1..20 {
+        print!("{}", i);
+        if is_prime(i) {
+            print!("*");
+        }
+        println!("");
+    }
+}
+
+/// Tests if the given number `n` is prime.
+fn is_prime(n: u64) -> bool {
+    // Note: there are nicer *and* faster ways to do a primality test. But that
+    // was not necessarily the point of this task.
+
+    // 1 is special and yes: 1 is not a prime!
+    if n <= 1 {
+        return false;
+    }
+
+    // Iterator through all possible divisors
+    for d in 2..n {
+        if n % d == 0 {
+            return false;
+        }
+    }
+
+    true
+}
+
+#[test]
+fn small_primes() {
+    assert!(is_prime(2));
+    assert!(is_prime(3));
+    assert!(is_prime(5));
+    assert!(is_prime(7));
+}
+
+#[test]
+fn small_composites() {
+    assert!(!is_prime(1));
+    assert!(!is_prime(4));
+    assert!(!is_prime(6));
+    assert!(!is_prime(8));
+    assert!(!is_prime(9));
+}
+
+#[test]
+fn large_primes() {
+    assert!(is_prime(1_300_769));
+    assert!(is_prime(1_300_297));
+    assert!(is_prime(7_367_287));
+}
+
+#[test]
+fn large_composites() {
+    assert!(!is_prime(908_209));
+    assert!(!is_prime(3_073_009));
+    assert!(!is_prime(4_897_369));
+}

aufgaben/sheet2/sol2/sort.rs

@@ -0,0 +1,42 @@
+fn main() {
+    let mut arr = [61, 21, 27, 79, 57, 60, 46, 42, 27, 92, 66, 26];
+
+    sort(&mut arr);
+    println!("{:?}", arr);
+}
+
+fn sort(arr: &mut [u64]) {
+    for start in 0..arr.len() {
+        let mut min_idx = start;
+
+        for i in start..arr.len() {
+            if arr[i] < arr[min_idx] {
+                min_idx = i;
+            }
+        }
+
+        // This is not a nice way to swap those elements. We should use
+        // `std::mem::swap()` or even better: `[T]::swap()`.
+        let tmp = arr[min_idx];
+        arr[min_idx] = arr[start];
+        arr[start] = tmp;
+    }
+}
+
+
+#[test]
+fn sort_array() {
+    let mut arr =  [
+        61, 21, 27, 79, 57, 60, 46, 92, 66, 26, 37, 15, 29, 70, 30, 55, 62, 81,
+        84, 35, 34, 52, 98, 50, 39, 42, 41, 24, 28, 64, 95, 47, 43, 23, 14, 71,
+        78, 86, 51, 20, 9, 1, 18, 17, 94, 33, 3, 91, 65, 2, 38, 59, 96, 8, 83,
+        19, 90, 63, 16, 58, 68, 48
+    ];
+    sort(&mut arr);
+    assert_eq!(&arr as &[u64], &[
+        1u64, 2, 3, 8, 9, 14, 15, 16, 17, 18, 19, 20, 21, 23, 24, 26, 27, 28, 29,
+        30, 33, 34, 35, 37, 38, 39, 41, 42, 43, 46, 47, 48, 50, 51, 52, 55, 57,
+        58, 59, 60, 61, 62, 63, 64, 65, 66, 68, 70, 71, 78, 79, 81, 83, 84, 86,
+        90, 91, 92, 94, 95, 96, 98,
+    ] as &[u64]);
+}

aufgaben/sheet2/sol3/count.rs

@@ -0,0 +1,19 @@
+//! Aufgabe 2.3
+
+fn main() {
+    let s = "The fat cat had a friend! ♥";
+    let count = count(s, 'a');
+    println!("{}", count);
+}
+
+
+fn count(haystack: &str, needle: char) -> u64 {
+    let mut count = 0;
+    for c in haystack.chars() {
+        if c == needle {
+            count += 1;
+        }
+    }
+
+    count
+}