low memory rework for day6 part 2

rust/day6/src/main.rs

@@ -1,5 +1,6 @@
 use std::fs;
 use std::io::BufRead;
+use std::collections::HashMap;
 
 static PATH: &'static str = "../../inputs/input-day6";
 
@@ -41,15 +42,50 @@ fn part1() {
     println!("total: {}", x.len());
 }
 
-fn part2() {
-    let mut x = load_file().unwrap();
+fn get_total(v: &HashMap<u8, u64>) -> u64 {
+    let mut total = 0;
 
-    for i in 0..256 {
-        run_day(&mut x);
-        println!("day: {} fish: {}", i+1, x.len());
+    for x in v {
+        total += x.1;
     }
 
-    println!("total: {}", x.len());
+    return total;
+}
+
+fn run_day_2(v: &HashMap<u8, u64>) -> HashMap<u8, u64> {
+    let mut state = HashMap::new();
+    for i in (0..=8).rev() {
+        if v.contains_key(&i) {
+            if let Some(cnt) = v.get(&i) {
+                if i == 0 {
+                    let c = state.entry(6).or_insert(0);
+                    *c += cnt;
+                    state.insert(8, *cnt);
+                } else {
+                    state.insert(i - 1, *cnt);
+                }
+            }
+        }
+    }
+
+    return state;
+}
+
+fn part2() {
+    let x = load_file().unwrap();
+
+    let mut fish = HashMap::<u8, u64>::new();
+
+    for val in x {
+        let n = fish.entry(val).or_insert(0);
+        *n += 1;
+    }
+
+    for _ in 0..256 {
+        fish = run_day_2(&fish);
+    }
+
+    println!("total: {}", get_total(&fish));
 }
 
 fn main() {