LeetCode 732. My Calendar III

Problem Statement

use std::collections::BTreeMap;

struct MyCalendarThree {
    events: BTreeMap<i32, i32>
}


/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl MyCalendarThree {

    fn new() -> Self {
        MyCalendarThree {
            events: BTreeMap::new()
        }
    }

    fn book(&mut self, start: i32, end: i32) -> i32 {
        self.events.entry(start).or_insert(0);
        self.events.entry(end).or_insert(0);
        *self.events.get_mut(&start).unwrap() += 1;
        *self.events.get_mut(&end).unwrap() -= 1;
        let (mut count, mut ans) = (0, 0);
        for (_k, v) in &self.events {
            count += *v;
            ans = std::cmp::max(count, ans);
        }
        return ans;
    }
}

/**
 * Your MyCalendarThree object will be instantiated and called as such:
 * let obj = MyCalendarThree::new();
 * let ret_1: i32 = obj.book(start, end);
 */