From 7ececd84fc4b85bdb147360a75847e923630ed6d Mon Sep 17 00:00:00 2001
From: Alpha Chen <alpha.chen@gmail.com>
Date: Sun, 2 Dec 2018 09:43:12 -0800
Subject: [PATCH] [2018][rust][1.1]

---
 2018/rust/src/main.rs | 41 +++++++++++++++++++++++++++++++++++++----
 1 file changed, 37 insertions(+), 4 deletions(-)

diff --git a/2018/rust/src/main.rs b/2018/rust/src/main.rs
index 3acbb2e..0d989e3 100644
--- a/2018/rust/src/main.rs
+++ b/2018/rust/src/main.rs
@@ -1,6 +1,7 @@
+use std::collections::HashMap;
 use std::io::{self, Read};
 
-fn day_1(input: &str, delimiter: &str) -> String {
+fn day_1_0(input: &str, delimiter: &str) -> String {
     let sum: i32 = input
         .split(delimiter)
         .flat_map(|change| change.parse::<i32>().ok())
@@ -9,14 +10,46 @@ fn day_1(input: &str, delimiter: &str) -> String {
 }
 
 #[test]
-fn test_day_1() {
-    assert_eq!(day_1("+1, -2, +3, +1", ", "), "3");
+fn test_day_1_0() {
+    assert_eq!(day_1_0("+1, -2, +3, +1", ", "), "3");
+}
+
+fn day_1_1(input: &str, delimiter: &str) -> String {
+    let mut seen = HashMap::new();
+    seen.insert(0, 1);
+
+    input
+        .split(delimiter)
+        .flat_map(|change| change.parse::<i32>().ok())
+        .cycle()
+        .scan((seen, 0), |(seen, freq), change| {
+            *freq += change;
+
+            let count = seen.entry(freq.clone()).or_insert(0);
+            *count += 1;
+
+            Some((freq.clone(), count.clone()))
+        })
+        .filter(|(_, count)| *count > 1)
+        .map(|(freq, _)| freq)
+        .next()
+        .unwrap()
+        .to_string()
+}
+
+#[test]
+fn test_day_1_1() {
+    assert_eq!(day_1_1("+1, -2, +3, +1", ", "), "2");
+    assert_eq!(day_1_1("+1, -1", ", "), "0");
+    assert_eq!(day_1_1("+3, +3, +4, -2, -4", ", "), "10");
+    assert_eq!(day_1_1("-6, +3, +8, +5, -6", ", "), "5");
+    assert_eq!(day_1_1("+7, +7, -2, -7, -4", ", "), "14");
 }
 
 fn main() {
     let mut input = String::new();
     io::stdin().read_to_string(&mut input).unwrap();
 
-    let output = day_1(&input, "\n");
+    let output = day_1_1(&input, "\n");
     println!("{}", output);
 }