sonar

#include <iostream>
#include <fstream>
#include <list>

#define not_yet_set -1;

using namespace std;

typedef long int lint;
typedef unsigned long long int ullint;

class target {
public:
    lint x, y;
};

// overloading this operator will help us on list sorting.
bool operator<(target a, target b)
{
    return (a.x == b.x) ? (a.x < b.x) : (a.y < b.y);
}

int main()
{
    lint N, w;
    ullint M1, M2;

    ifstream fin ("sonar.in");
    ofstream fout("sonar.out");

    target point;
    list<target> targets;

    // Beginning of Input
    fin >> N >> M1 >> M2;
    for(ullint i=0; i<M1; i++)
    {
        fin >> point.x >> w; // we are given the pos in x axis.
        point.y = N - w + 1; // process the signal to get the pos in y axis.
        targets.push_back(point);
    }

    for(ullint i=0; i<M2; i++)
    {
        fin >> point.y >> w;
        point.x = N - w + 1;
        targets.push_back(point);
    }
    // End of input.

    targets.sort();

    target last;
    last.x = last.y = not_yet_set;

    list<target>::iterator it;
    for(it = targets.begin(); it != targets.end(); it++)
    {
        //since the list is sorted, same instances of a point are near.
        if(it->x == last.x && it->y == last.y)
        {
            //if we find a double appearance, we must remove
            // the other  instances of that point from our list.
            it = targets.erase(it);
            it--;
            continue;
        }

        last.x = it->x;
        last.y = it->y;
    }

    //Output the final solution.
    fout << (int) targets.size() << "\n";
    for(it=targets.begin(); it != targets.end(); it++)
        fout << it->x << " " << it->y << "\n";

    //And pray for the testcases:
    // *pray* *pray*...

    fin.close();
    fout.close();
    return 0;
}