Add problem 1866: Number of Ways to Rearrange Sticks With K Sticks Vi…

…sible

src/lib.rs

@@ -1389,6 +1389,7 @@ pub mod problem_1862_sum_of_floored_pairs;
 pub mod problem_1863_sum_of_all_subset_xor_totals;
 pub mod problem_1864_minimum_number_of_swaps_to_make_the_binary_string_alternating;
 pub mod problem_1865_finding_pairs_with_a_certain_sum;
+pub mod problem_1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible;
 pub mod problem_1869_longer_contiguous_segments_of_ones_than_zeros;
 pub mod problem_1876_substrings_of_size_three_with_distinct_characters;
 pub mod problem_1877_minimize_maximum_pair_sum_in_array;

src/problem_1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible/iterative.rs

@@ -0,0 +1,46 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn rearrange_sticks(n: i32, k: i32) -> i32 {
+        const MODULUS: u64 = 1_000_000_007;
+
+        let n = n as u32;
+        let k = k as u32;
+        let mut cache = vec![0_u64; k as _].into_boxed_slice();
+
+        *cache.last_mut().unwrap() = 1;
+
+        let (first, rest) = cache.split_first_mut().unwrap();
+
+        for x in 1..u64::from(n) {
+            let mut target = &mut *first;
+
+            for next in &mut *rest {
+                *target = (x * *target + *next) % MODULUS;
+                target = next;
+            }
+
+            *target = (x * *target) % MODULUS;
+        }
+
+        cache[0] as _
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn rearrange_sticks(n: i32, k: i32) -> i32 {
+        Self::rearrange_sticks(n, k)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_1866_number_of_ways_to_rearrange_sticks_with_k_sticks_visible/mod.rs

@@ -0,0 +1,18 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn rearrange_sticks(n: i32, k: i32) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [((3, 2), 3), ((5, 5), 1)];
+
+        for ((n, k), expected) in test_cases {
+            assert_eq!(S::rearrange_sticks(n, k), expected);
+        }
+    }
+}