Add day 1 solution

2017/day/1/.gitignore

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+/target/
+**/*.rs.bk

2017/day/1/Cargo.lock

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+[[package]]
+name = "day1"
+version = "0.1.0"
+

2017/day/1/Cargo.toml

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+[package]
+name = "day1"
+version = "0.1.0"
+authors = ["Wesley Moore <wes@wezm.net>"]
+
+[dependencies]

2017/day/1/input

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+878938232157342756754254716586975125394865297349321236586574662994429894259828536842781199252169182743449435231194436368218599463391544461745472922916562414854275449983442828344463893618282425242643322822916857935242141636187859919626885791572268272442711988367762865741341467274718149255173686839265874184176985561996454253165784192929453678326937728571781212155346592432874244741816166328693958529938367575669663228335566435273484331452883175981955679335327231995452231118936393192583338222595982522833468533262224874637449624644318418748617949417939228988293391941457722641936417456243894182668197174255786445994567477582715692336249243254711653529871336129825735249667425238573952339922948214218872417858525199642194588448543565474847272984232637466664695217176358283788781843171636841215675851778984619377575696447366844854289534215286959727688419731976631323833892247438149829975856161755122857643731945913335556288817112993911694972667656914238999291831997163412548977649491227219477796124134958527843213824792685117696631512141241496451845758655276186597724748432996276498527911292531185292149948139724345841584782352214921634858734671118495424143437282979243347831258285851259579133433182387444656386679831584933397915132785411686688447731696776459621924821667112751789884987883991845818513249994767543526169463766975791464756526911587399764736557959464923353896921342944821833991457125256329564489631352268722457628514564128231487382111682976886838192412996932924373337524262135399256658638418515239876732866596731888779532573243713128238419234963195589987539467221517535272384899524386267268959484881379944796392255419838743164714275463459351741296586465213689853743856518583451849661592844879264196761867481258778393623584884535246239794178981387632311238115362178576899121425428114696158652976277392224226268242332589546757477683398264294929442592131949398261884548427951472128841328376819241955153423452531538413492577262348369581399925647624623868299468436859667152463974949436359589931136236247929554899679139746162554183855278713574244211854227829969443151478986413333429144796664423754818256172862812877688675514142265239992529776262844329188218189254491238956497568

2017/day/1/problem.txt

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+The captcha requires you to review a sequence of digits (your puzzle input) and find the sum of all digits that match the next digit in the list. The list is circular, so the digit after the last digit is the first digit in the list.
+
+For example:
+
+    1122 produces a sum of 3 (1 + 2) because the first digit (1) matches the second digit and the third digit (2) matches the fourth digit.
+    1111 produces 4 because each digit (all 1) matches the next.
+    1234 produces 0 because no digit matches the next.
+    91212129 produces 9 because the only digit that matches the next one is the last digit, 9.
+

2017/day/1/src/main.rs

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+use std::io::Read;
+use std::fs::File;
+
+fn main() {
+    let mut input = Vec::new();
+    let mut file = File::open("input").expect("unable to open input file");
+    file.read_to_end(&mut input).expect("error reading input");
+
+    println!("{}", captcha(&input));
+}
+
+fn captcha(input: &[u8]) -> u64 {
+    let digits = input.iter()
+        .take_while(|&&chr| chr >= 0x30 && chr <= 0x39)
+        .collect::<Vec<_>>();
+
+    let mut sum = 0;
+    for idx in 0..digits.len() {
+        if digits[idx] == digits[(idx + 1) % digits.len()] {
+            sum += *digits[idx] as u64 - 0x30;
+        }
+    }
+
+    sum
+}
+
+// 1122 produces a sum of 3 (1 + 2) because the first digit (1) matches the second digit and the
+// third digit (2) matches the fourth digit.
+#[test]
+fn test_example1() {
+    assert_eq!(captcha(b"1122"), 3);
+}
+
+// 1111 produces 4 because each digit (all 1) matches the next.
+#[test]
+fn test_example2() {
+    assert_eq!(captcha(b"1111"), 4);
+}
+
+// 1234 produces 0 because no digit matches the next.
+#[test]
+fn test_example3() {
+    assert_eq!(captcha(b"1234"), 0);
+}
+
+// 91212129 produces 9 because the only digit that matches the next one is the last digit, 9.
+#[test]
+fn test_example4() {
+    assert_eq!(captcha(b"91212129"), 9);
+}