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Arrays_MergeOverlappingIntervals.java
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Arrays_MergeOverlappingIntervals.java
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;
// https://practice.geeksforgeeks.org/problems/overlapping-intervals/0
// https://leetcode.com/problems/merge-intervals/
// https://leetcode.com/problems/merge-intervals/solution/
// https://www.youtube.com/watch?v=bom4wItgkt0
// https://www.youtube.com/watch?v=2JzRBPFYbKE&ab_channel=takeUforward (A GOOD VIDEO Explanation)
// https://leetcode.com/problems/merge-intervals/discuss/21222/A-simple-Java-solution (BEST post)
// https://leetcode.com/problems/non-overlapping-intervals/ (Very Similar problem, Arrays_NonOverlappingIntervals.java, only 3 line changes)
// https://www.lintcode.com/problem/meeting-rooms-ii/description (Very Similar problem)
public class Arrays_MergeOverlappingIntervals {
/* time complexity : O(Nlog(N)), space complexity : O(N) */
private static int[][] mergeAllOverlappingIntervals(int[][] intervals) {
List<int[]> mergedList = new ArrayList<>();
if (intervals == null || intervals.length == 0) {
return mergedList.toArray(new int[0][]);
}
/* each interval's 0th index represents the start time, 1st index represents the end time */
/* sorting on the starting time of the intervals */
Arrays.sort(intervals, Comparator.comparingInt(interval -> interval[0]));
int[] prevInterval = intervals[0];
mergedList.add(prevInterval);
for (int[] currInterval : intervals) {
/*if previous interval's endTime greater than current interval's startTime,
then there is a overlap, update the previous interval's endTime*/
if(prevInterval[1] >= currInterval[0]) { /* previous interval's end time is greater than or equals to current interval's start time, so overlaps */
prevInterval[1] = Math.max(prevInterval[1], currInterval[1]); /* Main difference from Arrays_NonOverlappingIntervals.java */
}
else {
/* no overlapping here,
add the current interval to the list and
make the current interval as previous interval
which will be used in the next round */
mergedList.add(currInterval);
prevInterval = currInterval;
}
}
return mergedList.toArray(new int[mergedList.size()][]);
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while(t-- > 0) {
int n = Integer.parseInt(br.readLine().trim());
String[] intervalInput = br.readLine().trim().split("\\s+");
int[][] intervals = new int[n][2];
for(int i = 0 ; i < n ; i++) {
intervals[i][0] = Integer.parseInt(intervalInput[i * 2]);
intervals[i][1] = Integer.parseInt(intervalInput[(i * 2) + 1]);
}
int[][] results = mergeAllOverlappingIntervals(intervals);
StringBuilder sb = new StringBuilder();
for (int[] result : results) {
sb.append(result[0]).append(" ").append(result[1]).append(" ");
}
System.out.println(sb.toString().trim());
}
}
}