Add 2016 day 4

2016/src/bin/day4.rs

@@ -0,0 +1,94 @@
+use std::collections::HashMap;
+use std::fs::File;
+use std::io::prelude::*;
+use std::path::Path;
+
+fn parse_end(last: &str) -> (i32, String) {
+    let mut sector_id = String::new();
+    let mut checksum = String::new();
+
+    for c in last.chars() {
+        if c.is_numeric() {
+            sector_id.push(c);
+            continue;
+        }
+
+        if c == '[' || c == ']' {
+            continue;
+        }
+
+        checksum.push(c);
+    }
+
+    (sector_id.parse::<i32>().unwrap(), checksum)
+}
+
+fn part1(lines: Vec<&str>) -> i32 {
+    let mut total = 0;
+
+    for line in lines {
+        let parts: Vec<&str> = line.split("-").collect();
+        let mut letter_freqs: HashMap<char, i32> = HashMap::new();
+
+        for i in 0..parts.len() - 1 {
+            for c in parts[i].chars() {
+                *letter_freqs.entry(c).or_insert(0) += 1;
+            }
+        }
+
+        let mut freqs: Vec<_> = letter_freqs.iter().collect();
+        freqs.sort_by(|a, b| {
+            if b.1 != a.1 {
+                b.1.cmp(a.1)
+            }
+            else {
+                a.0.cmp(b.0)
+            }});
+
+        let top5: String = freqs.iter().take(5).map(|f| f.0).collect();
+        let (sector_id, checksum) = parse_end(parts.last().unwrap());
+
+        if top5 == checksum {
+            total += sector_id;
+        }
+    }
+    total
+}
+
+fn part2(lines: Vec<&str>) {
+    for line in lines {
+        let parts: Vec<&str> = line.split("-").collect();
+        let (sector_id, _) = parse_end(parts.last().unwrap());
+        let mut new_strs = Vec::new();
+
+        for i in 0..parts.len() - 1 {
+            let mut new_str = String::new();
+            for c in parts[i].chars() {
+                new_str.push((((c as i32 - 'a' as i32 + sector_id) % 26) + ('a' as i32)) as u8 as char)
+            }
+            new_strs.push(new_str);
+        }
+
+        if new_strs.iter().any(|s| s.contains("north")) {
+            println!("strs {:?} sector_id {}", new_strs, sector_id);
+        }
+    }
+}
+
+fn main() {
+    let path = Path::new("input.txt");
+    let display = path.display();
+
+    let mut file = match File::open(&path) {
+        Err(why) => panic!("couldn't open {}: {}", display, why),
+        Ok(file) => file,
+    };
+
+    let mut s = String::new();
+    file.read_to_string(&mut s).unwrap();
+
+    let lines: Vec<&str> = s.trim().split("\n").collect();
+
+    println!("part 1 {}", part1(lines.clone()));
+    part2(lines);
+}