Add problem 2023: Number of Pairs of Strings With Concatenation Equal…

… to Target

src/lib.rs

@@ -1480,6 +1480,7 @@ pub mod problem_2012_sum_of_beauty_in_the_array;
 pub mod problem_2016_maximum_difference_between_increasing_elements;
 pub mod problem_2017_grid_game;
 pub mod problem_2022_convert_1d_array_into_2d_array;
+pub mod problem_2023_number_of_pairs_of_strings_with_concatenation_equal_to_target;
 pub mod problem_2024_maximize_the_confusion_of_an_exam;
 pub mod problem_2027_minimum_moves_to_convert_string;
 pub mod problem_2028_find_missing_observations;

src/problem_2023_number_of_pairs_of_strings_with_concatenation_equal_to_target/iterative.rs

@@ -0,0 +1,52 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn num_of_pairs(nums: Vec<String>, target: String) -> i32 {
+        let target = target.as_bytes();
+        let n = target.len();
+        let mut prefix_counts = vec![0_u8; n + 1].into_boxed_slice();
+
+        for num in &nums {
+            if target.starts_with(num.as_bytes()) {
+                prefix_counts[num.len()] += 1;
+            }
+        }
+
+        let mut result = 0;
+
+        for num in &nums {
+            if target.ends_with(num.as_bytes()) {
+                result += u16::from(prefix_counts[n - num.len()]);
+            }
+        }
+
+        if n % 2 == 0 {
+            let half = n / 2;
+            let (left, right) = target.split_at(half);
+
+            if left == right {
+                result -= u16::from(prefix_counts[half]);
+            }
+        }
+
+        i32::from(result)
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn num_of_pairs(nums: Vec<String>, target: String) -> i32 {
+        Self::num_of_pairs(nums, target)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_2023_number_of_pairs_of_strings_with_concatenation_equal_to_target/mod.rs

@@ -0,0 +1,26 @@
+pub mod iterative;
+
+pub trait Solution {
+    fn num_of_pairs(nums: Vec<String>, target: String) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            ((&["777", "7", "77", "77"] as &[_], "7777"), 4),
+            ((&["123", "4", "12", "34"], "1234"), 2),
+            ((&["1", "1", "1"], "11"), 6),
+            ((&["74", "1", "67", "1", "74"], "174"), 4),
+        ];
+
+        for ((nums, target), expected) in test_cases {
+            assert_eq!(
+                S::num_of_pairs(nums.iter().copied().map(str::to_string).collect(), target.to_string()),
+                expected,
+            );
+        }
+    }
+}