Here is solution in python, java, c++ and c programming - https://programmingoneonone.com/hackerrank-gridland-metro-problem-solution.html

In C++11, the output type needs to be updated from int to long long. Ensure this change is also applied within the main function.

C++ solution with long long instead of int

#include <bits/stdc++.h>

using namespace std;

string ltrim(const string &);
string rtrim(const string &);
vector<string> split(const string &);

/*
 * Complete the 'gridlandMetro' function below.
 *
 * The function is expected to return an INTEGER.
 * The function accepts following parameters:
 *  1. INTEGER n
 *  2. INTEGER m
 *  3. INTEGER k
 *  4. 2D_INTEGER_ARRAY track
 */
vector<vector<long long>> merge(vector<vector<long long>> tracks) {
    sort(tracks.begin(), tracks.end(), [](vector<long long>& a, vector<long long>& b) {
        return a[0] < b[0];
    });

    if (tracks.empty()) {
        return {};
    }

    vector<vector<long long>> merged_tracks;
    merged_tracks.push_back(tracks[0]);

    for (int i = 1; i < tracks.size(); i++) {
        long long last_end = merged_tracks.back()[1];
        long long current_start = tracks[i][0];
        long long current_end = tracks[i][1];

        if (current_start <= last_end + 1) { 
            merged_tracks.back()[1] = max(last_end, current_end);
        } else {
            merged_tracks.push_back(tracks[i]);
        }
    }
    return merged_tracks;
}

long long gridlandMetro(long long n, long long m, int k, vector<vector<int>> track) {

    long long totalsquares = n * m; 
    
    unordered_map<int, vector<vector<long long>>> mp; 

    for (const auto& i : track) {
        mp[i[0]].push_back({(long long)i[1], (long long)i[2]}); 
    }

    for (const auto& pair : mp) {
        const int row_index = pair.first;
        const vector<vector<long long>>& tracks_in_row = pair.second;
        
        vector<vector<long long>> merged_segments = merge(tracks_in_row);
        
        long long covered_cells_in_row = 0;
        
        for (const auto& segment : merged_segments) {
            covered_cells_in_row += segment[1] - segment[0] + 1; 
        }
        
        totalsquares -= covered_cells_in_row;
    }
    
    return totalsquares;
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    string first_multiple_input_temp;
    getline(cin, first_multiple_input_temp);

    vector<string> first_multiple_input = split(rtrim(first_multiple_input_temp));

    int n = stoi(first_multiple_input[0]);

    int m = stoi(first_multiple_input[1]);

    int k = stoi(first_multiple_input[2]);

    vector<vector<int>> track(k);

    for (int i = 0; i < k; i++) {
        track[i].resize(3);

        string track_row_temp_temp;
        getline(cin, track_row_temp_temp);

        vector<string> track_row_temp = split(rtrim(track_row_temp_temp));

        for (int j = 0; j < 3; j++) {
            int track_row_item = stoi(track_row_temp[j]);

            track[i][j] = track_row_item;
        }
    }

    long long result = gridlandMetro(n, m, k, track);

    fout << result << "\n";

    fout.close();

    return 0;
}

string ltrim(const string &str) {
    string s(str);

    s.erase(
        s.begin(),
        find_if(s.begin(), s.end(), not1(ptr_fun<int, int>(isspace)))
    );

    return s;
}

string rtrim(const string &str) {
    string s(str);

    s.erase(
        find_if(s.rbegin(), s.rend(), not1(ptr_fun<int, int>(isspace))).base(),
        s.end()
    );

    return s;
}

vector<string> split(const string &str) {
    vector<string> tokens;

    string::size_type start = 0;
    string::size_type end = 0;

    while ((end = str.find(" ", start)) != string::npos) {
        tokens.push_back(str.substr(start, end - start));

        start = end + 1;
    }

    tokens.push_back(str.substr(start));
		

    return tokens;
}

There's a mistake in the stub code given for C++14 - the function we need to write should return 'long long' type, not 'int'. Otherwise the results gets truncaded for the large input.

import java.util.ArrayList; import java.util.Collections; import java.util.HashMap; import java.util.Map; import java.util.Scanner;

public class Solution {

private static Map<Integer, ArrayList<Track>> tracksPerRow = new HashMap<Integer, ArrayList<Track>>();

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int numberOfRows = scanner.nextInt();
    int numberOfColumns = scanner.nextInt();
    int numberOfTracks = scanner.nextInt();

    for (int i = 0; i < numberOfTracks; i++) {
        int row = scanner.nextInt();
        int startColumn = scanner.nextInt();
        int endColumn = scanner.nextInt();
        fillMap(row, startColumn, endColumn);
    }
    scanner.close();

    sortTracksInsideRows_decreasingOrderOfStartColumn();
    long totalCellsWithTracks__exludingOverlaps = getTotalCellsWithTracks_exludingOverlaps();

    long spotsForLampPosts = (long) numberOfRows * numberOfColumns - (long) totalCellsWithTracks__exludingOverlaps;
    System.out.println(spotsForLampPosts);
}

private static void fillMap(int row, int start, int end) {
    Track track = new Track(start, end);

    if (!tracksPerRow.containsKey(row)) {
        ArrayList<Track> tracks = new ArrayList<Track>();
        tracks.add(track);
        tracksPerRow.put(row, tracks);
    } else {
        tracksPerRow.get(row).add(track);
    }
}

private static void sortTracksInsideRows_decreasingOrderOfStartColumn() {
    for (int row : tracksPerRow.keySet()) {
        Collections.sort(tracksPerRow.get(row));
    }
}

private static long getTotalCellsWithTracks_exludingOverlaps() {

    long totalCellsWithTracks__exludingOverlaps = 0;

    for (int row : tracksPerRow.keySet()) {

        int index = 0;

        ArrayList<Track> tracks = tracksPerRow.get(row);

        for (int i = 0; i < tracks.size(); i++) {

            if (index != 0 && tracks.get(index - 1).startColumn <= tracks.get(i).endColumn) {
                while (index != 0 && tracks.get(index - 1).startColumn <= tracks.get(i).endColumn) {

                    int minStart = Math.min(tracks.get(index - 1).startColumn, tracks.get(i).startColumn);
                    int maxEnd = Math.max(tracks.get(index - 1).endColumn, tracks.get(i).endColumn);

                    tracks.get(index - 1).startColumn = minStart;
                    tracks.get(index - 1).endColumn = maxEnd;
                    index--;
                }
            }
            else {
                tracks.set(index, tracks.get(i));
            }
            index++;
        }

        for (int j = 0; j < index; j++) {
            totalCellsWithTracks__exludingOverlaps += (long) tracks.get(j).endColumn
                    - (long) tracks.get(j).startColumn + 1;
        }
    }
    return totalCellsWithTracks__exludingOverlaps;
}

private static class Track implements Comparable<Track> {

    int startColumn;
    int endColumn;

    public Track(int startColumn, int endColumn) {
        this.startColumn = startColumn;
        this.endColumn = endColumn;
    }

    @Override
    public int compareTo(Track arg0) {
        return arg0.startColumn - this.startColumn;
    }
}

}