More iterators!

rs/src/day4.rs

@@ -1,50 +1,46 @@
 use itertools::izip;
 
 pub fn part1(data: &str) -> usize {
-    let lines = data.lines().collect::<Vec<_>>();
-    let mut result = 0;
-    for (y, line) in lines.iter().enumerate() {
-        for x in 0..line.len() {
-            for dy in -1..=1 {
-                for dx in -1..=1 {
-                    if "XMAS".bytes().enumerate().all(|(i, b)| {
-                        y.checked_add_signed(i as isize * dy)
-                            .and_then(|y| lines.get(y))
-                            .and_then(|line| {
-                                x.checked_add_signed(i as isize * dx)
-                                    .and_then(|x| line.as_bytes().get(x))
-                            })
-                            == Some(&b)
-                    }) {
-                        result += 1;
-                    }
-                }
-            }
-        }
-    }
-    result
+    let lines = &data.lines().collect::<Vec<_>>()[..];
+    lines
+        .iter()
+        .enumerate()
+        .flat_map(|(y, line)| {
+            (0..line.len()).flat_map(move |x| {
+                (-1..=1).flat_map(move |dy| {
+                    (-1..=1).filter(move |dx| {
+                        "XMAS".bytes().enumerate().all(|(i, b)| {
+                            y.checked_add_signed(i as isize * dy)
+                                .and_then(|y| lines.get(y))
+                                .zip(x.checked_add_signed(i as isize * dx))
+                                .and_then(|(line, x)| line.as_bytes().get(x))
+                                == Some(&b)
+                        })
+                    })
+                })
+            })
+        })
+        .count()
 }
 
 pub fn part2(data: &str) -> usize {
     let lines = data.lines().collect::<Vec<_>>();
-    let mut result = 0;
-    for (above, line, below) in izip!(&lines[..], &lines[1..], &lines[2..]) {
-        for (nw, ne, b, sw, se) in izip!(
-            above.bytes(),
-            above.bytes().skip(2),
-            line.bytes().skip(1),
-            below.bytes(),
-            below.bytes().skip(2)
-        ) {
-            if b == b'A'
-                && (nw == b'M' && se == b'S' || se == b'M' && nw == b'S')
-                && (ne == b'M' && sw == b'S' || sw == b'M' && ne == b'S')
-            {
-                result += 1;
-            }
-        }
-    }
-    result
+    izip!(&lines[..], &lines[1..], &lines[2..])
+        .flat_map(|(above, line, below)| {
+            izip!(
+                above.bytes(),
+                above.bytes().skip(2),
+                line.bytes().skip(1),
+                below.bytes(),
+                below.bytes().skip(2)
+            )
+            .filter(|&(nw, ne, b, sw, se)| {
+                b == b'A'
+                    && (nw == b'M' && se == b'S' || se == b'M' && nw == b'S')
+                    && (ne == b'M' && sw == b'S' || sw == b'M' && ne == b'S')
+            })
+        })
+        .count()
 }
 
 #[cfg(test)]