Add solution sheet7

aufgaben/sheet7/sol3/fold.rs

@@ -0,0 +1,19 @@
+fn main() {
+    // product
+    let fac_5 = (1..5).fold(1, |acc, x| acc * x);
+    assert_eq!(fac_5, (1..5).product());
+    println!("5! = {}", fac_5);
+
+    // max
+    let max = vec![3, 1, 4, 1, 5, 9, 2, 6]
+        .into_iter()
+        .fold(0, |acc, x| std::cmp::max(acc, x));
+    assert_eq!(max, 9);
+    println!("max: {}", max);
+
+    // all
+    let all_even = (1..9)
+        .fold(true, |acc, x| acc && (x % 2 == 0));
+    assert!(!all_even);
+    println!("all_even: {}", all_even);
+}