1 files changed, 99 insertions, 0 deletions

diff --git a/2021/day4/src/main.rs b/2021/day4/src/main.rs
new file mode 100644
index 0000000..4b6150f
--- /dev/null
+++ b/2021/day4/src/main.rs
@@ -0,0 +1,99 @@
+use std::env;
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn main() {
+    let args: Vec<String> = env::args().collect();
+
+    if args.len() != 2 {
+        eprintln!("Usage: {} filename", args[0]);
+        std::process::exit(1);
+    }
+
+    let filename = &args[1];
+
+    let file = File::open(filename).unwrap_or_else(|_| panic!("No such file: {}", filename));
+    let reader = BufReader::new(file);
+
+    let mut fd = reader.lines();
+    let mut called_numbers: Vec<i32> = Vec::new();
+
+    if let Ok(called_nums) = fd.next().unwrap() {
+        called_numbers = called_nums.split(",").map(|x| x.parse().unwrap()).collect();
+    }
+
+    fd.next(); /* Skip the empty line */
+
+    let mut boards: Vec<(Vec<(i32, bool)>, bool)> = Vec::new();
+
+    'outer: loop {
+        let mut miniboard: Vec<(i32, bool)> = Vec::new();
+        for _ in 0..5 {
+            /* New Board */
+            if let Some(maybe_line) = fd.next() {
+                if let Ok(line) = maybe_line {
+                    for (a, b) in line
+                        .split_whitespace()
+                        .map(|x| x.parse().unwrap())
+                        .zip([false].iter().cycle())
+                    {
+                        miniboard.push((a, *b));
+                    }
+                }
+            } else {
+                break 'outer;
+            }
+        }
+        boards.push((miniboard.clone(), false));
+        fd.next(); /* Skip the empty line */
+    }
+
+    for bingo in called_numbers {
+        for (board, _) in boards.iter_mut() {
+            for (num, mark) in board.iter_mut() {
+                if *num == bingo {
+                    *mark = true;
+                }
+            }
+        }
+
+        let mut count;
+        for (board, won) in boards.iter_mut() {
+            for row in 0..5 {
+                count = 0;
+                for i in row * 5..(row * 5) + 5 {
+                    if board[i].1 {
+                        count += 1;
+                    }
+                }
+                if count == 5 {
+                    *won = true;
+                }
+            }
+
+            for column in 0..5 {
+                count = 0;
+                for i in (0..5).map(|x| 5 * x + column) {
+                    if board[i].1 {
+                        count += 1;
+                    }
+                }
+                if count == 5 {
+                    *won = true;
+                }
+            }
+        }
+        if boards.len() == 1 {
+            let mut score: i32 = 0;
+            if let Some(board) = boards.get(0) {
+                for (winnynum, marked) in board.0.iter() {
+                    if !marked {
+                        score += winnynum;
+                    }
+                }
+                println!("score: {}", score * bingo);
+            }
+        }
+        boards.retain(|x| !x.1);
+    }
+}