From e94a2eb70482a255ba9fcd7fc42e099a777d4c5f Mon Sep 17 00:00:00 2001
From: June McEnroe <june@causal.agency>
Date: Sun, 4 Dec 2016 18:50:15 -0500
Subject: Use math to rotate in day 4

---
 src/bin/day04.rs | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

(limited to 'src/bin')

diff --git a/src/bin/day04.rs b/src/bin/day04.rs
index c6a9709..8e724c2 100644
--- a/src/bin/day04.rs
+++ b/src/bin/day04.rs
@@ -64,15 +64,12 @@ impl Room {
 }
 
 fn rotate(c: char, n: u32) -> char {
-    let mut c = c;
-    for _ in 0..n {
-        c = match c {
-            'a' ... 'y' => (c as u8 + 1) as char,
-            'z' => 'a',
-            _ => panic!("cannot rotate {}", c),
-        }
+    let c = c as u8 + (n % 26) as u8;
+    if c > b'z' {
+        (c - 26) as char
+    } else {
+        c as char
     }
-    c
 }
 
 fn solve1(input: &str) -> u32 {
-- 
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