problems: add „1338. Reduce Array Size to The Half“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/reduce-array-size-to-the-half.rs

@@ -0,0 +1,89 @@
+use std::collections::BTreeMap;
+
+struct Accumulator {
+    removed: usize,
+    removed_distinct: i32,
+}
+
+impl Accumulator {
+    fn new() -> Accumulator {
+        Accumulator { removed: 0, removed_distinct: 0 }
+    }
+
+    fn update(self, length: usize, count: i32) -> Accumulator {
+        if 2 * self.removed < length {
+            Accumulator {
+                removed: self.removed + count as usize,
+                removed_distinct: self.removed_distinct + 1,
+            }
+        } else {
+            self
+        }
+    }
+}
+
+impl Solution {
+    pub fn min_set_size(arr: Vec<i32>) -> i32 {
+        let mut counts = arr
+            .iter()
+            .fold(BTreeMap::<i32, i32>::new(), |mut acc: BTreeMap<i32, i32>, x: &i32| {
+                let current = *acc.get(x).unwrap_or(&0);
+                acc.insert(*x, current + 1);
+
+                acc
+            })
+            .iter()
+            .map(|(&x, &y)| { (x, y) })
+            .collect::<Vec<(i32, i32)>>();
+
+        counts
+            .sort_by(|&(_, y0), &(_, y1)| y1.cmp(&y0));
+
+        counts
+            .iter()
+            .fold(Accumulator::new(), |acc, &(_, count)| {
+                acc.update(arr.len(), count)
+            }).removed_distinct
+    }
+}
+
+struct Solution {}
+
+fn main() {
+    println!("Hello, world!");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example() {
+        assert_eq!(Solution::min_set_size(vec![3, 3, 3, 3, 5, 5, 5, 2, 2, 7]), 2);
+    }
+
+    #[test]
+    fn test_all_same() {
+        assert_eq!(Solution::min_set_size(vec![7, 7, 7, 7, 7, 7, 7, 7, 7, 7, 7]), 1);
+    }
+
+    #[test]
+    fn test_remove_exact_half() {
+        assert_eq!(Solution::min_set_size(vec![1, 1, 2, 2]), 1);
+    }
+
+    #[test]
+    fn test_remove_more_than_half() {
+        assert_eq!(Solution::min_set_size(vec![1, 1, 2, 2, 2]), 1);
+    }
+
+    #[test]
+    fn test_all_distinct() {
+        assert_eq!(Solution::min_set_size(vec![1, 2, 3, 4, 5, 6, 7]), 4);
+    }
+
+    #[test]
+    fn test_big_distinct() {
+        assert_eq!(Solution::min_set_size((1..=100).rev().collect()), 50);
+    }
+}