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

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);
    }
}