Add problem 1864: Minimum Number of Swaps to Make the Binary String A…

…lternating

src/lib.rs

@@ -1439,6 +1439,7 @@ pub mod problem_1855_maximum_distance_between_a_pair_of_values;
 pub mod problem_1859_sorting_the_sentence;
 pub mod problem_1860_incremental_memory_leak;
 pub mod problem_1861_rotating_the_box;
+pub mod problem_1864_minimum_number_of_swaps_to_make_the_binary_string_alternating;
 pub mod problem_1869_longer_contiguous_segments_of_ones_than_zeros;
 
 #[cfg(test)]

src/problem_1864_minimum_number_of_swaps_to_make_the_binary_string_alternating/greedy.rs

@@ -0,0 +1,44 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    fn fold_count(count: u16, c: u8) -> u16 {
+        count + u16::from(c) - u16::from(b'0')
+    }
+
+    pub fn min_swaps(s: String) -> i32 {
+        let n = s.len() as u16;
+        let ones = s.bytes().fold(0, Self::fold_count);
+        let zeros = n - ones;
+        let diff_plus_1 = (ones + 1).wrapping_sub(zeros);
+
+        if diff_plus_1 < 3 {
+            let even_ones = s.bytes().step_by(2).fold(0, Self::fold_count);
+
+            i32::from(match diff_plus_1 {
+                0 => even_ones,
+                1 => even_ones.min((n + 1) / 2 - even_ones),
+                _ => (n + 1) / 2 - even_ones,
+            })
+        } else {
+            -1
+        }
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn min_swaps(s: String) -> i32 {
+        Self::min_swaps(s)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_1864_minimum_number_of_swaps_to_make_the_binary_string_alternating/mod.rs

@@ -0,0 +1,18 @@
+pub mod greedy;
+
+pub trait Solution {
+    fn min_swaps(s: String) -> i32;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [("111000", 1), ("010", 0), ("1110", -1), ("1", 0)];
+
+        for (s, expected) in test_cases {
+            assert_eq!(S::min_swaps(s.to_string()), expected);
+        }
+    }
+}