Beginner struggling with Lee Algorithm on a 2D grid - c++

Question

I am trying to implement the Lee algorithm on a 2D grid. The flood loop is however stopping too early, claiming to have not found any more "empty" cells. I am completely stumped as to why.
#define WIDTH 6
#define HEIGHT 6
int gridArray[WIDTH][HEIGHT];
void InitialiseGrid() {
srand(time(NULL)); // initialise the randomiser
for (int y = 0; y < HEIGHT; y++) {
for (int x = 0; x < WIDTH; x++) {
if (rand() % 4 == 0)
gridArray[x][y] = -2;
else
gridArray[x][y] = -1;
}
}
}
bool foundEmpty = true;
bool foundEnd = false;
int it = 0;
while (foundEmpty && !foundEnd) {
DrawGrid();
cout << endl << endl;
for (int y = 0; y < HEIGHT; y++) {
for (int x = 0; x < WIDTH; x++) {
if (gridArray[x][y] == it) {
// initially assume neighbouring cells are not empty
foundEmpty = false;
// check east cell
if (x < WIDTH) {
int *e = &gridArray[x + 1][y];
if (*e == -1) {
*e = it + 1;
foundEmpty = true;
}
else if (*e == -3) {
foundEnd = true;
}
}
// check west cell
if (x > 0) {
int *w = &gridArray[x - 1][y];
if (*w == -1) {
*w = it + 1;
foundEmpty = true;
}
else if (*w == -3) {
foundEnd = true;
}
}
// check south cell
if (y < HEIGHT) {
int *s = &gridArray[x][y + 1];
if (*s == -1) {
*s = it + 1;
foundEmpty = true;
}
else if (*s == -3) {
foundEnd = true;
}
}
// check north cell
if (y > 0) {
int *n = &gridArray[x][y - 1];
if (*n == -1) {
*n = it + 1;
foundEmpty = true;
}
else if (*n == -3) {
foundEnd = true;
}
}
}
}
}
it++;
}
void DrawGrid() {
std::string message = "";
for (int y = 0; y < HEIGHT; y++) {
cout << endl;
for (int x = 0; x < WIDTH; x++) {
if (gridArray[x][y] == 0)
message = "start";
else if (gridArray[x][y] == -3)
message = "end";
else if (gridArray[x][y] == -2)
message = "X";
else
message = std::to_string(gridArray[x][y]);
cout << "|" << "\t" << message << "\t" << "|";
}
cout << endl;
}
}
The end on the path is specified by assigning a cell to -3. Cells that are blocked are -2. Cells that are empty are -1. The starting cell is 0.

Answer 1

Not sure what your problem is, but your algorithm seems to be solid. I have cleaned it a little and it seems to be working fine:
#include <iostream>
#include <string>
#include <iomanip>
#define WIDTH 7
#define HEIGHT 7
int gridArray[WIDTH][HEIGHT] =
{
{ -1,-1,-1,0,-2,-1,-2 },
{ -2,-1,-1,-1,-1,-2,-2 },
{ -2,-1,-1,-1,-1,-2,-2 },
{ -2,-2,-1,-1,-1,-2,-1 },
{ -1,-2,-2,-2,-1,-1,-2 },
{ -1,-2,-1,-1,-1,-2,-2 },
{ -2,-2,-3,-1,-1,-2,-2 }
};
void DrawGrid()
{
for (int x = 0; x < WIDTH; x++)
{
for (int y = 0; y < HEIGHT; y++)
{
std::string message;
if (gridArray[x][y] == 0)
message = "S";
else if (gridArray[x][y] == -3)
message = "E";
else if (gridArray[x][y] == -2)
message = "#";
else if (gridArray[x][y] == -1)
message = ".";
else
message = std::to_string(gridArray[x][y]);
std::cout << std::setw(3) << message << " ";
}
std::cout << std::endl << std::endl;
}
std::cout << std::endl << std::endl;
}
void SolveMaze()
{
bool foundEnd = false;
int it = 0;
while (!foundEnd)
{
bool foundEmpty = false;
for (int x = 0; x < WIDTH && !foundEnd; ++x)
{
for (int y = 0; y < HEIGHT; ++y)
{
if (gridArray[x][y] == it)
{
// check east cell
if (x < WIDTH - 1)
{
int &east = gridArray[x + 1][y];
if (east == -3)
{
foundEnd = true;
break;
}
else if (east == -1)
{
east = it + 1;
foundEmpty = true;
}
}
// check west cell
if (x > 0)
{
int &west = gridArray[x - 1][y];
if (west == -3)
{
foundEnd = true;
break;
}
else if (west == -1)
{
west = it + 1;
foundEmpty = true;
}
}
// check south cell
if (y < HEIGHT - 1)
{
int &south = gridArray[x][y + 1];
if (south == -3)
{
foundEnd = true;
break;
}
else if (south == -1)
{
south = it + 1;
foundEmpty = true;
}
}
// check north cell
if (y > 0)
{
int &north = gridArray[x][y - 1];
if (north == -3)
{
foundEnd = true;
break;
}
else if (north == -1)
{
north = it + 1;
foundEmpty = true;
}
}
}
}
}
if (!foundEnd && !foundEmpty)
{
std::cout << "This maze has no solution!" << std::endl << std::endl;
break;
}
it++;
}
}
int main()
{
DrawGrid();
SolveMaze();
DrawGrid();
system("pause");
return 0;
}