add solution for 6b

src/day6/b.txt

+4	1	15	12	0	9	9	5	5	8	7	3	14	5	12	3
\ No newline at end of file

src/day6/mod.rs

@@ -24,11 +24,11 @@ fn as_string(v: &Vec<u32>) -> String {
 fn detect_loop_for(start: &Vec<u32>) -> (u32, u32) {
     let mut current_state = start.clone();
 
-    let mut all_seen_states = HashSet::new();
+    let mut all_seen_states = HashMap::new();
     let mut iteration = 0;
     let mut cs: String = as_string(&current_state);
-    while !all_seen_states.contains(&cs) {
-        all_seen_states.insert(cs.clone());
+    while all_seen_states.get(&cs).is_none() {
+        all_seen_states.insert(cs.clone(), iteration);
         let (i, val) = calc_next(current_state.clone());
 
         current_state[i] = 0;
@@ -40,7 +40,8 @@ fn detect_loop_for(start: &Vec<u32>) -> (u32, u32) {
         iteration += 1;
         cs = as_string(&current_state);
     }
-    return (iteration, 0);
+    let cycle_size = iteration - *all_seen_states.get(&cs).unwrap();
+    return (iteration, cycle_size);
 }
 
 fn as_numbers(input: &String) -> Vec<u32> {
@@ -57,7 +58,8 @@ pub fn calc_day_6_a(input: String) -> u32 {
 
 #[wasm_bindgen]
 pub fn calc_day_6_b(input: String) -> u32 {
-    0
+    let input = as_numbers(&input);
+    return detect_loop_for(&input).1;
 }
 
 #[cfg(test)]
@@ -81,4 +83,9 @@ mod tests {
     fn it_should_calc_a() {
         assert_eq!(5, calc_day_6_a(String::from("0	2	7	0")))
     }
+
+    #[test]
+    fn it_should_calc_b() {
+        assert_eq!(4, calc_day_6_b(String::from("0	2	7	0")))
+    }
 }
\ No newline at end of file

tests/day6_test.rs

@@ -8,6 +8,6 @@ fn it_shoul_assert_result_of_day6_a() {
 
 #[test]
 fn it_shoul_assert_result_of_day6_b() {
-    assert_eq!(0, adventofcode_2017::results::day_6_b());
+    assert_eq!(2392, adventofcode_2017::results::day_6_b());
 }