Created
February 12, 2022 15:36
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Merge log files into one big log file
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| import java.time.LocalTime; | |
| import java.util.ArrayList; | |
| import java.util.Arrays; | |
| import java.util.Collections; | |
| import java.util.List; | |
| /** | |
| * Time complexity: O(m * n * log m) | |
| * Space complexity: O(m * n) | |
| * | |
| * m -> total number of log files | |
| * n -> average entries in each log file | |
| */ | |
| public class MergeLogFiles { | |
| public static List<String> mergeLogFiles(List<List<String>> logs) { | |
| // Special case | |
| if (logs == null || logs.size() == 0) { | |
| return Collections.emptyList(); | |
| } | |
| // List to store the sorted logs | |
| List<List<String>> sortedLogs = new ArrayList<>(); | |
| // Loop until there is only one element left in the logs | |
| // list which will represent the flat list of sorted items. | |
| while (logs.size() != 1) { | |
| // Clear the elements from the previous list | |
| sortedLogs.clear(); | |
| // Loop through all the individual log files | |
| for (int i = 0; i < logs.size(); i += 2) { | |
| // Add the last log file as is | |
| if (i == logs.size() - 1) { | |
| sortedLogs.add(logs.get(i)); | |
| } | |
| // Take two files at a time and sort them | |
| else { | |
| sortedLogs.add(merge(logs.get(i), logs.get(i + 1))); | |
| } | |
| } | |
| // Create a new list to avoid pointing to same reference | |
| logs = new ArrayList<>(sortedLogs); | |
| } | |
| return sortedLogs.get(0); | |
| } | |
| private static List<String> merge(List<String> left, List<String> right) { | |
| List<String> sortedList = new ArrayList<>(); | |
| // Pointers for both lists | |
| int i = 0; | |
| int j = 0; | |
| // Loop through the lists | |
| while (i < left.size() && j < right.size()) { | |
| // Get the timestamp from the log entry | |
| String leftTime = left.get(i).split(" ")[0]; | |
| String rightTime = right.get(j).split(" ")[0]; | |
| // Convert the time to LocalTime to compare | |
| LocalTime localTimeLeft = LocalTime.parse(leftTime); | |
| LocalTime localTimeRight = LocalTime.parse(rightTime); | |
| // Compare the timestamps and add smaller to the list | |
| if (localTimeLeft.isBefore(localTimeRight)) { | |
| sortedList.add(left.get(i)); | |
| i++; | |
| } else { | |
| sortedList.add(right.get(j)); | |
| j++; | |
| } | |
| } | |
| // Add remaining elements from left and right lists | |
| while (i < left.size()) { | |
| sortedList.add(left.get(i)); | |
| i++; | |
| } | |
| while (j < right.size()) { | |
| sortedList.add(right.get(j)); | |
| j++; | |
| } | |
| return sortedList; | |
| } | |
| public static void main(String[] args) { | |
| List<String> log1 = Arrays.asList( | |
| "07:35:02 log1 msg1", | |
| "07:35:03 log1 msg2", | |
| "07:35:03 log1 msg3", | |
| "07:35:15 log1 msg4" | |
| ); | |
| List<String> log2 = Arrays.asList( | |
| "07:34:43 log2 msg1", | |
| "07:35:16 log2 msg2", | |
| "07:36:15 log2 msg3" | |
| ); | |
| List<String> log3 = Arrays.asList( | |
| "06:53:48 log3 msg1", | |
| "07:23:27 log3 msg2", | |
| "07:33:27 log3 msg3", | |
| "07:34:27 log3 msg4", | |
| "07:35:28 log3 msg5" | |
| ); | |
| List<List<String>> logs = Arrays.asList(log1, log2, log3); | |
| List<String> sortedLogs = mergeLogFiles(logs); | |
| for (String sortedLog : sortedLogs) { | |
| System.out.println(sortedLog); | |
| } | |
| } | |
| } |
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