y2015d25

y2015/resources/25_input.txt

@@ -0,0 +1 @@
+To continue, please consult the code grid in the manual.  Enter the code at row 2981, column 3075.

y2015/src/bin/d25.rs

@@ -0,0 +1,9 @@
+use y2015::days::d25;
+
+fn main() {
+    part1();
+}
+
+fn part1() {
+    println!("{}", d25::process_part1(3075, 2981));
+}

y2015/src/days/d25.rs

@@ -0,0 +1,38 @@
+use utils::number::Number;
+
+// 31562160 too high
+pub fn process_part1(x: u32, y: u32) -> Number {
+    // the grid is actually a pyramid
+    //   1
+    //  2 3
+    // 4 5 6
+    // etc
+    // Num on top == 20151125
+    let mut current = Number::from(20151125);
+    let mut starting_y_idx = 2;
+    loop {
+        let mut x_idx = 1;
+        for y_idx in (1..=starting_y_idx).rev() {
+            current *= Number::from(252533);
+            current %= Number::from(33554393);
+            if x_idx == x && y_idx == y {
+                return current;
+            }
+            x_idx += 1;
+        }
+        starting_y_idx += 1;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1() {
+        let result = process_part1(6, 6);
+        assert_eq!(result, 27995004.into());
+        let result = process_part1(1, 2);
+        assert_eq!(result, 31916031.into());
+    }
+}

y2015/src/days/mod.rs

@@ -8,7 +8,14 @@ pub mod d15;
 pub mod d16;
 pub mod d17;
 pub mod d18;
+pub mod d19;
 pub mod d2;
+pub mod d20;
+pub mod d21;
+pub mod d22;
+pub mod d23;
+pub mod d24;
+pub mod d25;
 pub mod d3;
 pub mod d4;
 pub mod d5;
@@ -16,15 +23,3 @@ pub mod d6;
 pub mod d7;
 pub mod d8;
 pub mod d9;
-
-pub mod d19;
-
-pub mod d20;
-
-pub mod d21;
-
-pub mod d22;
-
-pub mod d23;
-
-pub mod d24;