Add exercise 212, 258, fix clippy warnings

e_378/src/main.rs

@@ -98,6 +98,8 @@ Here's the first pass through the algorithm using the original example:
 
 At this point you would start over at step 1 with the sequence `[5, 4, 4, 2, 1, 1, 1]`. After your second pass through the algorithm, your sequence will be `[3, 3, 1, 0, 0, 1]`, so start back at step 1 with this sequence. After your third pass you'll have `[2, 0, 0]`. On your fourth pass, you'll stop at step 5, because you'll have `N = 2` and an empty sequence (`[]`), and 2 > 0, so you will return false.
  */
+#![allow(dead_code)]
+#![allow(unused)]
 
 fn main() {}
 
@@ -122,7 +124,7 @@ fn warmup_4(i: i32, mut set: Vec<i32>) -> Vec<i32> {
 fn e_378(mut set: Vec<i32>) -> bool {
     loop {
         set = warmup_1(set);
-        if set.len() == 0 {
+        if set.is_empty() {
             break true;
         }
         set = warmup_2(set);