Day 2

2 files changed, 77 insertions, 6 deletions

diff --git a/2018/src/day2.rs b/2018/src/day2.rs
new file mode 100644
index 0000000..6564938
--- /dev/null
+++ b/2018/src/day2.rs
@@ -0,0 +1,64 @@
+use std::io;
+use std::io::BufRead;
+use std::collections::HashMap;
+
+fn close_enough(a: &str, b: &str) -> bool {
+    let mut num = 0;
+
+    for (ch1, ch2) in a.chars().zip(b.chars()) {
+        if ch1 != ch2 {
+            num += 1;
+            if num > 1 { return false; }
+        }
+    }
+
+    return num == 1;
+}
+
+pub fn main<T: BufRead>(reader: T) -> io::Result<()> {
+    let lines: Vec<String> = reader.lines().map(|l| l.unwrap()).collect();
+
+    let mut num2: i64 = 0;
+    let mut num3: i64 = 0;
+
+    for line in &lines {
+        let mut hist = HashMap::new();
+
+        for ch in line.chars() {
+            let value: i64 = *hist.get(&ch).unwrap_or(&0) + 1;
+            hist.insert(ch, value);
+        }
+
+        let mut have2 = false;
+        let mut have3 = false;
+        for &num in hist.values() {
+            if num == 2 { have2 = true; }
+            if num == 3 { have3 = true; }
+        }
+
+        num2 += have2 as i64;
+        num3 += have3 as i64;
+    }
+
+    println!("{}", num2 * num3);
+
+    // TODO: Can this be faster than n^2?
+    for line1 in &lines {
+        for line2 in &lines {
+            if !close_enough(&line1, &line2) { continue; }
+
+            let mut ans = String::new();
+
+            for (ch1, ch2) in line1.chars().zip(line2.chars()) {
+                if ch1 == ch2 {
+                    ans.push(ch1);
+                }
+            }
+
+            println!("{}", ans);
+            return Ok(())
+        }
+    }
+
+    Ok(())
+}
diff --git a/2018/src/main.rs b/2018/src/main.rs
index 7e683ca..162a56e 100644
--- a/2018/src/main.rs
+++ b/2018/src/main.rs
@@ -7,10 +7,12 @@ use std::process::exit;
 use argparse::{ArgumentParser, StoreTrue, Store};
 
 mod day1;
+mod day2;
 
 fn day_switch<T: BufRead>(day: i32, reader: T) -> io::Result<()> {
     match day {
         1 => day1::main(reader),
+        2 => day2::main(reader),
         _ => Err(Error::new(ErrorKind::Other, "Invalid day"))
     }
 }
@@ -65,13 +67,18 @@ fn main() -> io::Result<()> {
     }
 
     error_handler(||
-        match day_string.parse::<i32>() {
-            Ok(day) => run_day(day, &options),
-            Err(_) => {
-                for day in 1..1 {
-                    run_day(day, &options)?;
+        if day_string.len() == 0 {
+            for day in 1..3 {
+                run_day(day, &options)?;
+            }
+            Ok(())
+        } else {
+            match day_string.parse::<i32>() {
+                Ok(day) => run_day(day, &options),
+                Err(_) => {
+                    println!("Invalid day argument");
+                    exit(1)
                 }
-                Ok(())
             }
         }
     )