Complete day 9 part 2

diff --git a/src/day09.rs b/src/day09.rs
index e80700f6d3f1f50725fc975c6843fd4ce78c27a9..34f4202f5f3dfda5f7955b81eaf5c6fc857573f0 100644 (file)
--- a/src/day09.rs
+++ b/src/day09.rs
@@ -34,6 +34,57 @@ fn fragment(disk: &mut Vec<DiskMap>) {
     }
 }
 
+fn compact(disk: &mut [DiskMap]) {
+    let mut lp = 0;
+    let mut ls = 0;
+    let mut rp = disk.len() - 1;
+    let mut rs = 0;
+    let mut id = disk[rp];
+    loop {
+        // size up rightmost disk region not yet considered
+        while disk[rp] == id && rp > 0 {
+            rs += 1;
+            rp -= 1;
+        }
+        // if we've reached start of disk, quit
+        if rp == 0 {
+            break;
+        }
+        // size up leftmost free regions
+        // lp <= rp: cf. '00....1111', can't capture full free region otw
+        while ls < rs && lp <= rp {
+            match disk[lp] {
+                Some(_) => {
+                    ls = 0;
+                    lp += 1;
+                }
+                None => {
+                    ls += 1;
+                    lp += 1;
+                }
+            }
+        }
+        // if we found a region big enough to fit the disk region, move
+        if ls == rs {
+            for i in disk.iter_mut().take(lp).skip(lp - ls) {
+                *i = id;
+            }
+            for i in disk.iter_mut().take(rp + rs + 1).skip(rp + 1) {
+                *i = None;
+            }
+        }
+        // move ptr to next disk region
+        while disk[rp].is_none() {
+            rp -= 1;
+        }
+        // reset
+        id = disk[rp];
+        lp = 0;
+        ls = 0;
+        rs = 0;
+    }
+}
+
 fn checksum(disk: &[DiskMap]) -> u64 {
     disk.iter()
         .zip(0..)
@@ -52,7 +103,9 @@ pub fn part1() {
 }
 
 pub fn part2() {
-    let n = 0;
+    let mut disk = parse(input());
+    compact(&mut disk);
+    let n = checksum(&disk);
     println!("Day 9 Part 2: {}", n);
 }
 
@@ -93,10 +146,10 @@ mod test {
     #[rustfmt::skip]
     #[test]
     fn test_fragment() {
-        let mut map = parse(INPUT_STR);
-        fragment(&mut map);
+        let mut disk = parse(INPUT_STR);
+        fragment(&mut disk);
         assert_eq!(
-            map,
+            disk,
             vec![
                 Some(0), Some(0),
                 Some(9), Some(9),
@@ -115,10 +168,98 @@ mod test {
         )
     }
 
+    #[rustfmt::skip]
+    #[test]
+    fn test_compact() {
+        let mut disk = parse(INPUT_STR);
+        compact(&mut disk);
+        assert_eq!(
+            disk,
+            vec![
+                Some(0), Some(0),
+                Some(9), Some(9),
+                Some(2),
+                Some(1), Some(1), Some(1),
+                Some(7), Some(7), Some(7),
+                None,
+                Some(4), Some(4),
+                None,
+                Some(3), Some(3), Some(3),
+                None, None, None, None,
+                Some(5), Some(5), Some(5), Some(5),
+                None,
+                Some(6), Some(6), Some(6), Some(6),
+                None, None, None, None, None,
+                Some(8), Some(8), Some(8), Some(8),
+                None, None,
+            ],
+        );
+
+        disk = vec![
+            Some(0), Some(0),
+            None, None, None,
+            Some(1), Some(1), Some(1),
+            None, None, None, None,
+            None, None, None,
+            Some(3), Some(3), Some(3),
+            None,
+            Some(4), Some(4),
+            None,
+            Some(5), Some(5), Some(5), Some(5),
+            None,
+            Some(6), Some(6), Some(6), Some(6),
+            None,
+            Some(7), Some(7), Some(7),
+            None,
+            Some(8), Some(8), Some(8), Some(8),
+            Some(9), Some(9)
+        ];
+        compact(&mut disk);
+        assert_eq!(
+            disk,
+            vec![
+                Some(0), Some(0),
+                Some(9), Some(9),
+                None,
+                Some(1), Some(1), Some(1),
+                Some(8), Some(8), Some(8), Some(8),
+                Some(7), Some(7), Some(7),
+                Some(3), Some(3), Some(3),
+                None,
+                Some(4), Some(4),
+                None,
+                Some(5), Some(5), Some(5), Some(5),
+                None,
+                Some(6), Some(6), Some(6), Some(6),
+                None, None, None, None, None, None,
+                None, None, None, None, None,
+            ],
+        );
+
+        disk = vec![
+            Some(0), Some(0),
+            None, None, None, None, 
+            Some(1), Some(1), Some(1), Some(1),
+        ];
+        compact(&mut disk);
+        assert_eq!(
+            disk,
+            vec![
+                Some(0), Some(0),
+                Some(1), Some(1), Some(1), Some(1),
+                None, None, None, None, 
+            ],
+        );
+    }
+
     #[test]
     fn test_checksum() {
-        let mut map = parse(INPUT_STR);
-        fragment(&mut map);
-        assert_eq!(checksum(&map), 1928)
+        let mut disk = parse(INPUT_STR);
+        fragment(&mut disk);
+        assert_eq!(checksum(&disk), 1928);
+
+        disk = parse(INPUT_STR);
+        compact(&mut disk);
+        assert_eq!(checksum(&disk), 2858);
     }
 }