Add problem 2327: Number of People Aware of a Secret

src/lib.rs

@@ -1731,6 +1731,7 @@ pub mod problem_2320_count_number_of_ways_to_place_houses;
 pub mod problem_2321_maximum_score_of_spliced_array;
 pub mod problem_2325_decode_the_message;
 pub mod problem_2326_spiral_matrix_iv;
+pub mod problem_2327_number_of_people_aware_of_a_secret;
 pub mod problem_2331_evaluate_boolean_binary_tree;
 pub mod problem_2335_minimum_amount_of_time_to_fill_cups;
 pub mod problem_2336_smallest_number_in_infinite_set;

src/problem_2327_number_of_people_aware_of_a_secret/mod.rs

@@ -0,0 +1,18 @@
+pub mod sliding_window;
+
+pub trait Solution {
+    fn people_aware_of_secret(n: i32, delay: i32, forget: i32) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [((6, 2, 4), 5), ((4, 1, 3), 6), ((684, 18, 496), 653_668_527)];
+
+        for ((n, delay, forget), expected) in test_cases {
+            assert_eq!(S::people_aware_of_secret(n, delay, forget), expected);
+        }
+    }
+}

src/problem_2327_number_of_people_aware_of_a_secret/sliding_window.rs

@@ -0,0 +1,70 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    const MODULUS: u32 = 1_000_000_007;
+
+    fn assign_add_sub(target: &mut u32, add: u32, subtract: u32) {
+        *target += add;
+        *target += Self::MODULUS - subtract;
+
+        if *target >= Self::MODULUS {
+            *target -= Self::MODULUS;
+        }
+
+        if *target >= Self::MODULUS {
+            *target -= Self::MODULUS;
+        }
+    }
+
+    pub fn people_aware_of_secret(n: i32, delay: i32, forget: i32) -> i32 {
+        let n = n as u32 as usize;
+
+        assert!(n <= 1000);
+
+        let delay = delay as u32 as usize;
+        let forget = forget as u32 as usize;
+        let mut cache = [0_u32; 1000];
+
+        cache[0] = 1;
+
+        let mut sum = 0_u32;
+        let new_offset = delay;
+        let old_offset = forget;
+
+        for day in 1..n {
+            let spreading_count = cache.get(day.wrapping_sub(old_offset)).copied().unwrap_or(0);
+
+            Self::assign_add_sub(
+                &mut sum,
+                cache.get(day.wrapping_sub(new_offset)).copied().unwrap_or(0),
+                spreading_count,
+            );
+
+            cache[day] = sum;
+        }
+
+        cache[n - forget..n].iter().fold(0_u32, |mut sum, &x| {
+            sum += x;
+
+            sum.checked_sub(Self::MODULUS).unwrap_or(sum)
+        }) as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn people_aware_of_secret(n: i32, delay: i32, forget: i32) -> i32 {
+        Self::people_aware_of_secret(n, delay, forget)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}