Add day 4 rust

.gitignore

@@ -1,2 +1,3 @@
 *.in
 *.ex*
+day??

day04.rs

@@ -0,0 +1,42 @@
+use std::collections::HashSet;
+use std::io::{self, BufRead};
+
+fn main() {
+    // Part 1
+    let mut part1 = 0;
+    let cards: Vec<usize> = io::stdin()
+        .lock()
+        .lines()
+        .map(|line| {
+            let line = line.unwrap();
+            let (_, card) = line.split_once(": ").unwrap();
+            let (winning, owned) = card.split_once(" | ").unwrap();
+
+            let winning: HashSet<i32> = winning
+                .split_whitespace()
+                .flat_map(str::parse)
+                .collect();
+
+            let owned: HashSet<i32> = owned
+                .split_whitespace()
+                .flat_map(str::parse)
+                .collect();
+
+            let count = winning.intersection(&owned).count();
+
+            part1 += 1 << (count - 1);
+            count
+        })
+        .collect();
+
+    // Part 2
+    let mut dp = vec![1; cards.len()];
+    let part2: i32 = (0..cards.len())
+        .map(|i| {
+            dp[i] += dp[i - cards[cards.len() - i - 1]..i].iter().sum::<i32>();
+            dp[i]
+        })
+        .sum();
+
+    println!("{} {}", part1, part2);
+}