Algoritmul lui Lee

#include <iostream>
#include <fstream>
#include <queue>

using namespace std;

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

int di[4] = {0,  0, 1, -1};
int dj[4] = {1, -1, 0,  1};

int N, M, Map[180][180];
int startx, starty, stopx, stopy;

queue < pair < int, int > > coada;

void Citire()
{
    fin >> N >> M;
    for(int i = 1; i <= M; i++)
    {
        int x, y;
        fin >> x >> y;
        Map[x][y] = -1; //Map[x][y] e obstacol
    }
    fin >> startx >> starty;
    fin >> stopx >> stopy;
}

bool OK(int i, int j)
{
    if(i < 1 || j < 1 || i > N || j > N) // Daca depaseste granitele
        return false;
    if(Map[i][j] == -1) // Daca intalneste un obstacol
        return false;
    return true;
}

void Lee()
{
    int i, j, i_urmator, j_urmator;
    Map[startx][starty] = 1;
    coada.push(make_pair(startx, starty)); //Inserare pozitie de pornire in coada
    while(!coada.empty()) // Verifica daca coada este libera
    {
        i = coada.front().first; // Extrage coordonata x a primului punct din coada
        j = coada.front().second; // Extrage coordonata y a primului punct din coada
        coada.pop();
        for(int dir = 0; dir < 4; dir++)
        {
            i_urmator = i + di[dir];
            j_urmator = j + dj[dir];
            if(OK(i_urmator, j_urmator) && Map[i_urmator][j_urmator] < 1)
            {
                Map[i_urmator][j_urmator] = Map[i][j] + 1;
                coada.push(make_pair(i_urmator, j_urmator));
            }
        }
    }
}

int main()
{
    Citire();
    Lee();
    fout << Map[stopx][stopy];
    return 0;
}