cj.java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RangeMerger {
    
    // Simple class to represent an integer range with inclusive start and end
    static class Range {
        int start;
        int end;
        
        public Range(int start, int end) {
            this.start = start;
            this.end = end;
        }
        
        // Calculate the number of integers in this range (inclusive)
        public int size() {
            return end - start + 1;
        }
    }
    
    public static void main(String[] args) {
        final String INPUT_PATH = "input.txt";
        List<Range> freshRanges = new ArrayList<>();
        
        // Regex pattern to match lines in format: "number-number"
        // Supports optional whitespace and negative numbers
        Pattern rangePattern = Pattern.compile("^\\s*(-?\\d+)\\s*-\\s*(-?\\d+)\\s*$");
        
        // Read the input file line by line
        try (BufferedReader reader = new BufferedReader(new FileReader(INPUT_PATH))) {
            String line;
            while ((line = reader.readLine()) != null) {
                Matcher matcher = rangePattern.matcher(line);
                
                if (matcher.matches()) {
                    // Parse the two numbers from the matched groups
                    int a = Integer.parseInt(matcher.group(1));
                    int b = Integer.parseInt(matcher.group(2));
                    freshRanges.add(new Range(a, b));
                } else {
                    // Warn about invalid lines
                    System.err.println("Skipping invalid range line: " + line);
                }
            }
        } catch (IOException e) {
            System.err.println("Error reading file: " + e.getMessage());
            return;
        }
        
        // Sort ranges by their starting value
        freshRanges.sort((r1, r2) -> Integer.compare(r1.start, r2.start));
        
        // Merge overlapping or adjacent ranges
        List<Range> merged = new ArrayList<>();
        for (Range r : freshRanges) {
            if (merged.isEmpty() || r.start > merged.get(merged.size() - 1).end + 1) {
                // Range is disjoint (doesn't overlap with last range)
                // Add it as a new separate range
                merged.add(new Range(r.start, r.end));
            } else {
                // Range overlaps or is adjacent to the last range
                // Extend the last range's end to cover both ranges
                Range last = merged.remove(merged.size() - 1);
                int newEnd = Math.max(last.end, r.end);
                merged.add(new Range(last.start, newEnd));
            }
        }
        
        // Calculate total count of unique integers across all merged ranges
        int uniqueCount = 0;
        for (Range r : merged) {
            uniqueCount += r.size();
        }
        
        System.out.println(uniqueCount);
    }
}