Finish day 4

day_04/README.md

@@ -0,0 +1,85 @@
+# --- Day 4: Ceres Search ---
+
+"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
+
+As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: `XMAS`.
+
+This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of `XMAS` - you need to find all of them. Here are a few ways `XMAS` might appear, where irrelevant characters have been replaced with `.`:
+
+```
+..X...
+.SAMX.
+.A..A.
+XMAS.S
+.X....
+```
+
+The actual word search will be full of letters instead. For example:
+
+```
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
+```
+
+In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:
+
+```
+....XXMAS.
+.SAMXMS...
+...S..A...
+..A.A.MS.X
+XMASAMX.MM
+X.....XA.A
+S.S.S.S.SS
+.A.A.A.A.A
+..M.M.M.MM
+.X.X.XMASX
+```
+
+Take a look at the little Elf's word search. How many times does XMAS appear?
+
+Your puzzle answer was 2524.
+# --- Part Two ---
+
+The Elf looks quizzically at you. Did you misunderstand the assignment?
+
+Looking for the instructions, you flip over the word search to find that this isn't actually an XMAS puzzle; it's an X-MAS puzzle in which you're supposed to find two MAS in the shape of an X. One way to achieve that is like this:
+
+```
+M.S
+.A.
+M.S
+```
+
+Irrelevant characters have again been replaced with . in the above diagram. Within the X, each MAS can be written forwards or backwards.
+
+Here's the same example from before, but this time all of the X-MASes have been kept instead:
+
+```
+.M.S......
+..A..MSMS.
+.M.S.MAA..
+..A.ASMSM.
+.M.S.M....
+..........
+S.S.S.S.S.
+.A.A.A.A..
+M.M.M.M.M.
+..........
+```
+
+In this example, an X-MAS appears 9 times.
+
+Flip the word search from the instructions back over to the word search side and try again. How many times does an X-MAS appear?
+
+Your puzzle answer was 1873.
+
+Both parts of this puzzle are complete! They provide two gold stars: **

day_04/src/crossword.rs

@@ -28,55 +28,101 @@ impl<'a> CrosswordCell<'a> {
         self.value_by_index(self.x, self.y)
     }
 
-    fn take(&self, num_of_letters: usize, direction: (isize, isize)) -> String {
+    fn take(&self, num_of_letters: usize, direction: (isize, isize), start: isize) -> String {
         let mut word = String::new();
 
-        for i in 0..num_of_letters {
+        let end = start + num_of_letters as isize;
-            let x = self.x as isize + (i as isize * direction.1);
+
-            let y = self.y as isize + (i as isize * direction.0);
+        for i in start..end {
+            let x = self.x as isize + (i * direction.1);
+            let y = self.y as isize + (i * direction.0);
             if x < 0
                 || x >= self.crossword.width as isize
                 || y < 0
                 || y >= self.crossword.height as isize
             {
+                if i < 0 {
+                    continue;
+                } else {
                     break;
                 }
+            }
             word.push(self.value_by_index(x as usize, y as usize));
         }
 
         word
     }
 
+    const DIRECTION_N: (isize, isize) = (-1, 0);
     pub fn n(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (-1, 0))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_N, 0)
     }
 
+    pub fn n2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_N, start)
+    }
+
+    const DIRECTION_NE: (isize, isize) = (-1, 1);
     pub fn ne(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (-1, 1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_NE, 0)
     }
 
+    pub fn ne2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_NE, start)
+    }
+
+    const DIRECTION_E: (isize, isize) = (0, 1);
     pub fn e(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (0, 1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_E, 0)
     }
 
+    pub fn e2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_E, start)
+    }
+
+    const DIRECTION_SE: (isize, isize) = (1, 1);
     pub fn se(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (1, 1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_SE, 0)
     }
 
+    pub fn se2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_SE, start)
+    }
+
+    const DIRECTION_S: (isize, isize) = (1, 0);
     pub fn s(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (1, 0))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_S, 0)
     }
 
+    pub fn s2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_S, start)
+    }
+
+    const DIRECTION_SW: (isize, isize) = (1, -1);
     pub fn sw(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (1, -1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_SW, 0)
     }
 
+    pub fn sw2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_SW, start)
+    }
+
+    const DIRECTION_W: (isize, isize) = (0, -1);
     pub fn w(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (0, -1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_W, 0)
     }
 
+    pub fn w2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_W, start)
+    }
+
+    const DIRECTION_NW: (isize, isize) = (-1, -1);
     pub fn nw(&self, num_of_letters: usize) -> String {
-        self.take(num_of_letters, (-1, -1))
+        self.take(num_of_letters, CrosswordCell::DIRECTION_NW, 0)
+    }
+
+    pub fn nw2(&self, num_of_letters: usize, start: isize) -> String {
+        self.take(num_of_letters, CrosswordCell::DIRECTION_NW, start)
     }
 }
 
@@ -198,6 +244,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).n(1), "5");
         assert_eq!(crossword.cell(1, 1).n(2), "52");
         assert_eq!(crossword.cell(1, 1).n(3), "52");
+        assert_eq!(crossword.cell(1, 1).n2(3, 1), "2");
+        assert_eq!(crossword.cell(1, 1).n2(3, 0), "52");
+        assert_eq!(crossword.cell(1, 1).n2(3, -1), "852");
+        assert_eq!(crossword.cell(1, 1).n2(3, -2), "85");
     }
 
     #[test]
@@ -207,6 +257,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).ne(1), "5");
         assert_eq!(crossword.cell(1, 1).ne(2), "53");
         assert_eq!(crossword.cell(1, 1).ne(3), "53");
+        assert_eq!(crossword.cell(1, 1).ne2(3, 1), "3");
+        assert_eq!(crossword.cell(1, 1).ne2(3, 0), "53");
+        assert_eq!(crossword.cell(1, 1).ne2(3, -1), "753");
+        assert_eq!(crossword.cell(1, 1).ne2(3, -2), "75");
     }
 
     #[test]
@@ -216,6 +270,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).e(1), "5");
         assert_eq!(crossword.cell(1, 1).e(2), "56");
         assert_eq!(crossword.cell(1, 1).e(3), "56");
+        assert_eq!(crossword.cell(1, 1).e2(3, 1), "6");
+        assert_eq!(crossword.cell(1, 1).e2(3, 0), "56");
+        assert_eq!(crossword.cell(1, 1).e2(3, -1), "456");
+        assert_eq!(crossword.cell(1, 1).e2(3, -2), "45");
     }
 
     #[test]
@@ -225,6 +283,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).se(1), "5");
         assert_eq!(crossword.cell(1, 1).se(2), "59");
         assert_eq!(crossword.cell(1, 1).se(3), "59");
+        assert_eq!(crossword.cell(1, 1).se2(3, 1), "9");
+        assert_eq!(crossword.cell(1, 1).se2(3, 0), "59");
+        assert_eq!(crossword.cell(1, 1).se2(3, -1), "159");
+        assert_eq!(crossword.cell(1, 1).se2(3, -2), "15");
     }
 
     #[test]
@@ -234,6 +296,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).s(1), "5");
         assert_eq!(crossword.cell(1, 1).s(2), "58");
         assert_eq!(crossword.cell(1, 1).s(3), "58");
+        assert_eq!(crossword.cell(1, 1).s2(3, 1), "8");
+        assert_eq!(crossword.cell(1, 1).s2(3, 0), "58");
+        assert_eq!(crossword.cell(1, 1).s2(3, -1), "258");
+        assert_eq!(crossword.cell(1, 1).s2(3, -2), "25");
     }
 
     #[test]
@@ -243,6 +309,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).sw(1), "5");
         assert_eq!(crossword.cell(1, 1).sw(2), "57");
         assert_eq!(crossword.cell(1, 1).sw(3), "57");
+        assert_eq!(crossword.cell(1, 1).sw2(3, 1), "7");
+        assert_eq!(crossword.cell(1, 1).sw2(3, 0), "57");
+        assert_eq!(crossword.cell(1, 1).sw2(3, -1), "357");
+        assert_eq!(crossword.cell(1, 1).sw2(3, -2), "35");
     }
 
     #[test]
@@ -252,6 +322,10 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).w(1), "5");
         assert_eq!(crossword.cell(1, 1).w(2), "54");
         assert_eq!(crossword.cell(1, 1).w(3), "54");
+        assert_eq!(crossword.cell(1, 1).w2(3, 1), "4");
+        assert_eq!(crossword.cell(1, 1).w2(3, 0), "54");
+        assert_eq!(crossword.cell(1, 1).w2(3, -1), "654");
+        assert_eq!(crossword.cell(1, 1).w2(3, -2), "65");
     }
 
     #[test]
@@ -261,5 +335,9 @@ mod tests {
         assert_eq!(crossword.cell(1, 1).nw(1), "5");
         assert_eq!(crossword.cell(1, 1).nw(2), "51");
         assert_eq!(crossword.cell(1, 1).nw(3), "51");
+        assert_eq!(crossword.cell(1, 1).nw2(3, 1), "1");
+        assert_eq!(crossword.cell(1, 1).nw2(3, 0), "51");
+        assert_eq!(crossword.cell(1, 1).nw2(3, -1), "951");
+        assert_eq!(crossword.cell(1, 1).nw2(3, -2), "95");
     }
 }

day_04/src/main.rs

@@ -2,6 +2,8 @@
 //
 // Run command: cargo run ./input.txt
 
+#![allow(dead_code)]
+
 use std::env;
 use std::error::Error;
 use std::fs::File;
@@ -64,9 +66,23 @@ fn main() -> Result<(), Box<dyn Error>> {
     }
 
     println!(
-        "Count of the work '{}' in crossword: {}",
+        "Count of the word '{}' in crossword: {}",
         word_to_find, count
     );
 
+    let mas = "MAS".to_owned();
+    let mas_rev = mas.chars().rev().collect::<String>();
+    let mut count = 0;
+    for cell in crossword.iter_cells() {
+        let se_word = cell.se2(3, -1);
+        let sw_word = cell.sw2(3, -1);
+
+        if (se_word == mas || se_word == mas_rev) && (sw_word == mas || sw_word == mas_rev) {
+            count += 1;
+        }
+    }
+
+    println!("Count of the MAS Xes in crossword: {}", count);
+
     Ok(())
 }