1 files changed, 107 insertions, 0 deletions
diff --git a/2021/day4/src/main.rs b/2021/day4/src/main.rs
new file mode 100644
index 0000000..4b2f9b3
--- /dev/null
+++ b/2021/day4/src/main.rs
@@ -0,0 +1,107 @@
+use std::fs::File;
+use std::io::{BufRead, BufReader};
+
+fn part1(grids: &Vec<Vec<u32>>, mut inputs: Vec<u32>) -> u32 {
+    let mut values = Vec::<u32>::new();
+
+    for _ in 0..4 {
+        values.push(inputs.remove(0));
+    }
+
+    let mut winner: i8 = -1;
+    for input in inputs {
+        if winner >= 0 {
+            break;
+        }
+        values.push(input);
+        for i in 0..grids.len() {
+            // Search by rows
+            for j in [0, 5, 10, 15, 20] {
+                let mut n = 0;
+                for k in 0..5 {
+                    let x = grids[i][j + k];
+                    if values.iter().any(|&i| i == x) {
+                        n += 1;
+                    }
+                }
+                if n == 5 {
+                    winner = i as i8;
+                }
+            }
+
+            // Search by cols
+            if winner < 0 {
+                for j in 0..5 {
+                    let mut n = 0;
+                    for k in [0, 5, 10, 15, 20] {
+                        let x = grids[i][j + k];
+                        if values.iter().any(|&i| i == x) {
+                            n += 1;
+                        }
+                    }
+                    if n == 5 {
+                        winner = i as i8;
+                    }
+                }
+            }
+
+            if winner >= 0 {
+                break;
+            }
+        }
+    }
+
+    let mut sum = 0;
+    for x in &grids[winner as usize] {
+        if values.iter().any(|&i| i == *x) {
+            continue;
+        }
+
+        sum += x;
+    }
+
+    sum * values.pop().unwrap()
+}
+
+fn main() -> std::io::Result<()> {
+    let file = File::open("input.txt")?;
+    let reader = BufReader::new(file);
+    let mut lines = reader.lines();
+
+    let inputs: Vec<_> = lines
+        .next()
+        .unwrap()
+        .unwrap()
+        .trim()
+        .split(',')
+        .map(|x| x.parse::<u32>().unwrap())
+        .collect::<Vec<u32>>();
+
+    let mut grids: Vec<Vec<u32>> = vec![];
+    let mut n: usize = 0;
+
+    lines.next(); // Ignore the first empty line
+    while let Some(line) = lines.next() {
+        let mut line = line.unwrap();
+        grids.push(Vec::with_capacity(5 * 5));
+
+        for _ in 0..5 {
+            grids[n].extend(
+                line.trim()
+                    .split(' ')
+                    .filter(|x| !x.is_empty())
+                    .map(|x| x.parse::<u32>().unwrap())
+                    .collect::<Vec<u32>>(),
+            );
+            line = match lines.next() {
+                Some(x) => x.unwrap(),
+                None => "".to_string(),
+            };
+        }
+        n += 1;
+    }
+
+    println!("{}", part1(&grids, inputs.clone()));
+
+    Ok(())
+}