rs: add «2402. Meeting Rooms III»

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

rs/meeting-rooms-iii.rs

@@ -0,0 +1,132 @@
+use std::cmp;
+use std::collections::BinaryHeap;
+
+struct MinHeap<T: Ord> {
+    heap: BinaryHeap<cmp::Reverse<T>>,
+}
+
+impl<T: Ord> MinHeap<T> {
+    pub fn new() -> Self {
+        Self {
+            heap: BinaryHeap::new(),
+        }
+    }
+
+    pub fn push(&mut self, item: T) {
+        self.heap.push(cmp::Reverse(item));
+    }
+
+    pub fn pop(&mut self) -> Option<T> {
+        self.heap.pop().map(|cmp::Reverse(item)| item)
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.heap.is_empty()
+    }
+
+    pub fn peek(&self) -> Option<&T> {
+        self.heap.peek().map(|cmp::Reverse(item)| item)
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+struct Meeting {
+    start: i64,
+    end: i64,
+}
+
+impl Meeting {
+    fn duration(&self) -> i64 {
+        self.end - self.start
+    }
+}
+
+impl From<Vec<i32>> for Meeting {
+    fn from(m: Vec<i32>) -> Self {
+        Self {
+            start: m[0].into(),
+            end: m[1].into(),
+        }
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord)]
+struct Allocation {
+    end_time: i64,
+    room: usize,
+}
+
+impl Allocation {
+    fn new(end_time: i64, room: usize) -> Self {
+        Self { end_time, room }
+    }
+}
+
+struct Solution {}
+impl Solution {
+    pub fn most_booked(n: i32, meetings: Vec<Vec<i32>>) -> i32 {
+        let mut meetings: Vec<Meeting> = meetings.into_iter().map(|m| m.into()).collect();
+        meetings.sort();
+
+        let mut free_rooms: MinHeap<usize> = MinHeap::new();
+        (0..n as usize).for_each(|i| free_rooms.push(i));
+        let mut nonfree_rooms: MinHeap<Allocation> = MinHeap::new();
+
+        let mut counts: Vec<i32> = vec![0; n as usize];
+        for meeting in &meetings {
+            // re-add rooms that have been freed
+            while let Some(allocation) = nonfree_rooms.peek() {
+                if allocation.end_time > meeting.start {
+                    break;
+                }
+
+                free_rooms.push(allocation.room);
+                nonfree_rooms.pop();
+            }
+
+            // occupy a room with the meeting
+            if let Some(free_room) = free_rooms.pop() {
+                nonfree_rooms.push(Allocation::new(meeting.end, free_room));
+                counts[free_room] += 1;
+            } else if let Some(allocation) = nonfree_rooms.pop() {
+                nonfree_rooms.push(Allocation::new(
+                    allocation.end_time + meeting.duration(),
+                    allocation.room,
+                ));
+                counts[allocation.room] += 1;
+            }
+        }
+
+        (0..counts.len()).fold(0, |best_idx, idx| {
+            if counts[idx] > counts[best_idx] {
+                idx
+            } else {
+                best_idx
+            }
+        }) as i32
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        assert_eq!(
+            Solution::most_booked(2, vec![vec![0, 10], vec![1, 5], vec![2, 7], vec![3, 4]]),
+            0
+        );
+    }
+
+    #[test]
+    fn example_2() {
+        assert_eq!(
+            Solution::most_booked(
+                3,
+                vec![vec![1, 20], vec![2, 10], vec![3, 5], vec![4, 9], vec![6, 8]]
+            ),
+            1
+        );
+    }
+}