Day 2

2018/src/day2.rs

@@ -0,0 +1,109 @@
+use std::collections::{HashMap, HashSet};
+use std::iter::{Iterator, Zip};
+use std::str;
+
+const INPUT: &str = include_str!("input/day2.txt");
+
+type CharCount = HashMap<char, u32>;
+
+fn count_chars(s: &str) -> CharCount {
+    let mut counts: HashMap<char, u32> = HashMap::new();
+    for c in s.chars() {
+        let mut count = counts.entry(c).or_insert(0);
+        *count += 1;
+    }
+    counts
+}
+
+fn has_double(cc: &CharCount) -> bool {
+    for v in cc.values() {
+        if v == &2 {
+            return true;
+        }
+    }
+    false
+}
+
+fn has_triple(cc: &CharCount) -> bool {
+    for v in cc.values() {
+        if v == &3 {
+            return true;
+        }
+    }
+    false
+}
+
+pub fn part1() -> u32 {
+    let mut twos = 0;
+    let mut threes = 0;
+    for line in str::lines(INPUT) {
+        let cc = count_chars(line);
+        if has_double(&cc) {
+            twos += 1;
+        }
+        if has_triple(&cc) {
+            threes += 1;
+        }
+    }
+    twos * threes
+}
+
+fn difference_count(s1: &str, s2: &str) -> usize {
+    let mut d = 0;
+    let mut i1 = s1.chars();
+    let mut i2 = s2.chars();
+
+    loop {
+        let c1 = i1.next();
+        let c2 = i2.next();
+        match (c1, c2) {
+            (Some(a), Some(b)) => {
+                if a != b {
+                    d += 1;
+                }
+            }
+            (Some(_), None) => d += 1,
+            (None, Some(_)) => d += 1,
+            (None, None) => break,
+        }
+    }
+    d
+}
+
+fn common_chars<'a>(s1: &'a str, s2: &'a str) -> String {
+    let mut common = "".to_owned();
+    let mut i1 = s1.chars();
+    let mut i2 = s2.chars();
+
+    loop {
+        let c1 = i1.next();
+        let c2 = i2.next();
+
+        match (c1, c2) {
+            (Some(a), Some(b)) => {
+                if a == b {
+                    common.push(a);
+                }
+            }
+            (Some(_), None) => panic!("s1.len() != s2.len()"),
+            (None, Some(_)) => panic!("s1.len() != s2.len()"),
+            (None, None) => break,
+        }
+    }
+    common
+}
+
+pub fn part2() -> String {
+    let mut pairs = HashSet::new();
+    for l1 in str::lines(INPUT) {
+        for l2 in str::lines(INPUT) {
+            pairs.insert((l1, l2));
+        }
+    }
+    for (s1, s2) in pairs {
+        if difference_count(s1, s2) == 1 {
+            return common_chars(s1, s2);
+        }
+    }
+    panic!("No solution")
+}

2018/src/main.rs

@@ -1,6 +1,9 @@
 mod day1;
+mod day2;
 
 fn main() {
     println!("{}", day1::part1());
     println!("{}", day1::part2());
+    println!("{}", day2::part1());
+    println!("{}", day2::part2());
 }