diff --git a/src/lib.rs b/src/lib.rs
index 14171f8..e9c92c6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -35,4 +35,5 @@ pub mod long_pressed_name;
 pub mod can_win_nim;
 pub mod hamming_distance;
 pub mod word_pattern;
-pub mod update_matrix;
\ No newline at end of file
+pub mod update_matrix;
+pub mod prison_cells_after_n_days;
\ No newline at end of file
diff --git a/src/prison_cells_after_n_days.rs b/src/prison_cells_after_n_days.rs
new file mode 100644
index 0000000..7d7d0c3
--- /dev/null
+++ b/src/prison_cells_after_n_days.rs
@@ -0,0 +1,33 @@
+pub fn prison_after_n_days(cells: Vec<i32>, n: i32) -> Vec<i32> {
+    let mut cells = cells;
+    let mut start = (n - 1) % 14 + 1;
+    while start > 0 {
+        start -= 1;
+        let mut next = vec![0; 8];
+        for i in 1..7 {
+            next[i] = if cells[i - 1] == cells[i + 1] { 1 } else { 0 };
+        }
+        cells = next;
+    }
+    cells
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn example_1() {
+        assert_eq!(
+            prison_after_n_days(vec![0, 1, 0, 1, 1, 0, 0, 1], 7),
+            vec![0, 0, 1, 1, 0, 0, 0, 0]
+        );
+    }
+
+    #[test]
+    fn example_2() {
+        assert_eq!(
+            prison_after_n_days(vec![1, 0, 0, 1, 0, 0, 1, 0], 1000000000),
+            vec![0, 0, 1, 1, 1, 1, 1, 0]
+        );
+    }
+}