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leetcode_java/src/main/java/LeetCodeJava/Sort/MeetingRooms2.java
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| @@ -0,0 +1,138 @@ | ||
| package LeetCodeJava.Sort; | ||
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| import java.util.Arrays; | ||
| import java.util.Comparator; | ||
| import java.util.PriorityQueue; | ||
| import java.util.Queue; | ||
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| // https://leetcode.com/problems/meeting-rooms-ii/description/ | ||
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| public class MeetingRooms2 { | ||
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| // V0 | ||
| // IDEA : ARRAY SORT + BOUNDARY OP | ||
| // https://github.com/yennanliu/CS_basics/blob/master/leetcode_python/Sort/meeting-rooms-ii.py#L90 | ||
| public int minMeetingRooms(int[][] intervals) { | ||
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| final int n = intervals.length; | ||
| int ans = 0; | ||
| int[] starts = new int[n]; | ||
| int[] ends = new int[n]; | ||
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| for (int i = 0; i < n; ++i) { | ||
| starts[i] = intervals[i][0]; | ||
| ends[i] = intervals[i][1]; | ||
| } | ||
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| Arrays.sort(starts); | ||
| Arrays.sort(ends); | ||
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| // J points to ends | ||
| for (int i = 0, j = 0; i < n; ++i) | ||
| if (starts[i] < ends[j]) | ||
| ++ans; | ||
| else | ||
| ++j; | ||
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| return ans; | ||
| } | ||
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| // V0' | ||
| // TODO : validate below | ||
| // IDEA : ARRAY SORT + BOUNDARY OP | ||
| // https://github.com/yennanliu/CS_basics/blob/master/leetcode_python/Sort/meeting-rooms-ii.py#L90 | ||
| // IDEA : CREATE A NEW ARRAY WITH | ||
| // (intervals[i][0], 1) // if start point | ||
| // (intervals[i][1], -1) // if end point | ||
| // public int minMeetingRooms(int[][] intervals) { | ||
| // | ||
| // if (intervals == null || intervals.length == 0) { | ||
| // return 0; | ||
| // } | ||
| // | ||
| // // Convert intervals to a list of start and end points | ||
| // int n = intervals.length; | ||
| // int[][] points = new int[n * 2][2]; | ||
| // for (int i = 0; i < n; i++) { | ||
| // points[i * 2] = new int[]{intervals[i][0], 1}; // start point | ||
| // points[i * 2 + 1] = new int[]{intervals[i][1], -1}; // end point | ||
| // } | ||
| // | ||
| // // Sort the points based on their time, if time is same then process end point first | ||
| // Arrays.sort(points, new Comparator<int[]>() { | ||
| // public int compare(int[] a, int[] b) { | ||
| // if (a[0] != b[0]) { | ||
| // return a[0] - b[0]; | ||
| // } else { | ||
| // return a[1] - b[1]; | ||
| // } | ||
| // } | ||
| // }); | ||
| // | ||
| // // Use a min heap to track the end times of ongoing meetings | ||
| // PriorityQueue<Integer> minHeap = new PriorityQueue<>(); | ||
| // int rooms = 0; | ||
| // int maxRooms = 0; | ||
| // | ||
| // for (int[] point : points) { | ||
| // if (point[1] == 1) { // start point | ||
| // rooms++; | ||
| // } else { // end point | ||
| // rooms--; | ||
| // } | ||
| // maxRooms = Math.max(maxRooms, rooms); | ||
| // } | ||
| // | ||
| // return maxRooms; | ||
| // } | ||
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| // V1 | ||
| // IDEA : HEAP (PQ) (priority queue) | ||
| // https://walkccc.me/LeetCode/problems/253/#__tabbed_1_2 | ||
| public int minMeetingRooms_1(int[][] intervals) { | ||
| Arrays.sort(intervals, (a, b) -> (a[0] - b[0])); | ||
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| // Store the end times of each room. | ||
| Queue<Integer> minHeap = new PriorityQueue<>(); | ||
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| for (int[] interval : intervals) { | ||
| // There's no overlap, so we can reuse the same room. | ||
| if (!minHeap.isEmpty() && interval[0] >= minHeap.peek()) | ||
| minHeap.poll(); | ||
| minHeap.offer(interval[1]); | ||
| } | ||
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| return minHeap.size(); | ||
| } | ||
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| // V2 | ||
| // IDEA : SORT | ||
| // https://walkccc.me/LeetCode/problems/253/#__tabbed_1_2 | ||
| public int minMeetingRooms_2(int[][] intervals) { | ||
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| final int n = intervals.length; | ||
| int ans = 0; | ||
| int[] starts = new int[n]; | ||
| int[] ends = new int[n]; | ||
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| for (int i = 0; i < n; ++i) { | ||
| starts[i] = intervals[i][0]; | ||
| ends[i] = intervals[i][1]; | ||
| } | ||
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| Arrays.sort(starts); | ||
| Arrays.sort(ends); | ||
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| // J points to ends | ||
| for (int i = 0, j = 0; i < n; ++i) | ||
| if (starts[i] < ends[j]) | ||
| ++ans; | ||
| else | ||
| ++j; | ||
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| return ans; | ||
| } | ||
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| } |