Add problem 3039: Apply Operations to Make String Empty

Author: EFanZh

src/lib.rs

@@ -2057,6 +2057,7 @@ pub mod problem_3028_ant_on_the_boundary;
 pub mod problem_3033_modify_the_matrix;
 pub mod problem_3035_maximum_palindromes_after_operations;
 pub mod problem_3038_maximum_number_of_operations_with_the_same_score_i;
+pub mod problem_3039_apply_operations_to_make_string_empty;
 
 #[cfg(test)]
 mod test_utilities;

src/problem_3039_apply_operations_to_make_string_empty/greedy.rs

@@ -0,0 +1,49 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl Solution {
+    pub fn last_non_empty_string(s: String) -> String {
+        let mut states = [(0_u32, 0_u32); 26];
+
+        (0..).zip(s.bytes()).for_each(|(i, c)| {
+            let state = &mut states[usize::from(c) - usize::from(b'a')];
+
+            state.0 += 1;
+            state.1 = i;
+        });
+
+        let max_count = states.iter().fold(0, |max, &(count, _)| max.max(count));
+        let mut buffer = [(0, 0); 26];
+        let mut length = 0;
+
+        (b'a'..).zip(&states).for_each(|(c, &(count, i))| {
+            if count == max_count {
+                buffer[length] = (i, c);
+                length += 1;
+            }
+        });
+
+        let buffer = &mut buffer[..length];
+
+        buffer.sort_unstable_by_key(|&(i, _)| i);
+
+        buffer.iter().map(|&(_, c)| char::from(c)).collect()
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn last_non_empty_string(s: String) -> String {
+        Self::last_non_empty_string(s)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}

src/problem_3039_apply_operations_to_make_string_empty/mod.rs

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