Why is this BFS queue size so large? - c++

Question

I am recently working with BFS algorithm. I made a maze solving program with this algorithm. here is my code:
#include<iostream>
#include<cmath>
#include<sstream>
#include<vector>
#include<queue>
#include <unistd.h>
using namespace std;
int m,n;
inline int indexFor(int x,int y) {
return (x-1) + m*(y-1);
}
int main() {
FILE *file = fopen("test_case","r"); // test_case file
//build maze
fscanf(file,"%d",&m);
fscanf(file,"%d",&n);
vector<int> grid((m+1)*(n+1));
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
int k;
fscanf(file,"%d",&k);
grid[indexFor(i,j)] = k;
}
}
int startX,startY,endX,endY;
fscanf(file,"%d",&startX);
fscanf(file,"%d",&startY);
fscanf(file,"%d",&endX);
fscanf(file,"%d",&endY);
//bfs starts
queue<int> x,y;
x.push(1);
y.push(1);
vector<int> visited((m+1)*(n+1),0);
vector<vector<int>> path_track((m+1)*(n+1),vector<int>(2,0));
while(x.size()>0) {
int k = x.front(), l = y.front();
x.pop();
y.pop();
visited[indexFor(k,l)]=1;
// this part for printing each steps
cout << "\033[2J\033[H";
cout << "queue size: " << x.size()<<endl;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(visited[indexFor(i,j)]==1) cout << "* ";
else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
usleep(10);
if(k-1>0) {
if(grid[indexFor(k-1,l)] != 1 && visited[indexFor(k-1,l)]!=1) {
x.push(k-1);
y.push(l);
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
if((k+1)<=m) {
if(grid[indexFor(k+1,l)] != 1 && visited[indexFor(k+1,l)]!=1) {
x.push(k+1);
y.push(l);
//cout << "Path_track: "<<x.back() << ", " << y.back() << " : " << k << ", " << l <<endl;
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
if(l-1>0) {
if(grid[indexFor(k,l-1)] != 1 && visited[indexFor(k,l-1)]!=1) {
x.push(k);
y.push(l-1);
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
if(l+1<=n) {
if(grid[indexFor(k,l+1)] != 1 && visited[indexFor(k,l+1)]!=1) {
x.push(k);
y.push(l+1);
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
}
cout << "\033[2J\033[H";
vector<vector<int>> path;
path.push_back({endX,endY});
while(endX!=0&&endY!=0) {
int kx = endX, ky = endY;
endX = path_track[indexFor(kx,ky)][0];
endY = path_track[indexFor(kx,ky)][1];
path.push_back({endX,endY});
}
path.pop_back();
if(path[path.size()-1][0] == startX && path[path.size()-1][1] == startY)
{
for(vector<int> l:path) grid[indexFor(l[0],l[1])] = 8;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(grid[indexFor(i,j)]==8) {
cout << "X ";
} else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
} else {
cout << "No path found\n";
for(vector<int> l:path) grid[indexFor(l[0],l[1])] = 8;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(grid[indexFor(i,j)]==8) {
cout << "X ";
} else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
}
//cout<<path_track[indexFor(2,2)][0]<<","<<path_track[indexFor(2,2)][1]<<endl;
return 0;
}
I made a maze_generator for this problem which is :
#include <iostream>
#include <vector>
using namespace std;
int m,n;
inline int indexFor(int x,int y) {
return m * (x-1) + (y-1);
}
int main() {
srand(time(nullptr));
FILE * f = fopen("test_case","w");
cin >> m;
cin >> n;
vector<int> grid(m*n,0);
fprintf(f,"%d %d\n",m,n);
for(int i = 0; i<grid.size();i++) {
int k = (rand()%7);
if(i == 0 || i==grid.size()-1 ) k = 0;
grid[i] = k<5?0:1;
}
grid[indexFor(m,n)] = 0;
for(int i = 1;i<=m;i++) {
for(int j = 1; j<=n;j++) {
cout << grid[indexFor(i,j)] << " ";
fprintf(f,"%d ",grid[indexFor(i,j)]);
}
cout<<endl;
fprintf(f,"\n");
}
fprintf(f,"1 1\n%d %d",m,n);
return 0;
}
which generated this test_case:
21 50
0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 1 1 0 1 0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 1 0 0 1 0 1
0 0 0 1 0 0 0 0 0 0 1 0 0 1 0 0 0 1 0 0 0 1 1 1 0 0 1 0 1 0 0 0 1 0 0 0 1 0 1 1 0 0 0 1 0 1 0 0 0 0
1 1 1 0 0 1 0 1 0 0 0 1 0 0 0 1 0 1 1 0 0 0 1 0 1 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 1 0 0 0 0
0 1 0 1 0 0 0 0 0 0 0 1 0 0 1 0 0 0 0 1 0 0 0 1 1 0 0 0 0 1 0 1 1 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0
0 0 1 1 0 0 0 0 1 0 1 1 0 1 1 0 0 0 0 1 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 0 0 0 1 1 1 1 0 0 0
0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 0 0 0 1 1 1 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0 1 0 0 0 0 1 0
0 1 0 1 0 0 0 0 0 0 0 0 0 1 0 1 1 1 1 0 0 0 1 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0
0 1 0 0 0 0 1 0 0 1 0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 0 0 0 0 0 1 1 0 0
0 0 0 0 1 0 0 0 0 0 1 1 0 0 1 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 1 1 1 0 1 1 0 1
0 0 0 0 1 1 0 0 0 1 0 0 1 1 0 0 0 0 0 0 0 1 1 1 0 1 1 0 1 0 1 1 0 0 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 1
1 1 1 0 1 1 0 1 0 1 1 0 0 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0
0 0 1 0 0 0 0 1 0 1 0 1 0 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0
0 1 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 0 1 0 1
1 0 1 0 0 0 0 0 1 1 0 0 0 1 0 0 0 1 0 0 0 0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1
0 0 0 1 0 1 0 1 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 1 1 0 0 1 1 0 0 0 1 1 0 0 0 1 1 1 1 0 0 1 0 0 0 0 0 0
0 0 1 1 0 0 1 1 0 0 0 1 1 0 0 0 1 1 1 1 0 0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0
0 1 0 0 0 0 0 0 1 0 1 0 0 0 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 1
1 1 1 0 0 0 0 0 0 0 1 0 0 0 0 0 1 1 1 0 0 0 0 0 0 1 0 0 1 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0
0 0 0 0 1 0 0 1 1 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 0 0 0 0 0 0 0 0 0 1 1 1 1 0 0 1 0 1 1 1 0 0
1 1
21 50
In the test case the last two line represents starting and ending point for the maze. In case for maze 0 indicates free path and 1 indicates wall. 1st line denotes the size of maze.
Problem is that when I solve it the queue size jumped to 130k+ for this particular test_case. Is there something I missing? or it is normal?

Answer 1

I solved the problem. Looks like i needed use another array for queue mapping to check if a point is already queued. Here is the final solution:
#include<iostream>
#include<cmath>
#include<sstream>
#include<vector>
#include<queue>
#include <unistd.h>
using namespace std;
int m,n;
inline int indexFor(int x,int y) {
return (x-1) + m*(y-1);
}
int main() {
FILE *file = fopen("test_case","r");
fscanf(file,"%d",&m);
fscanf(file,"%d",&n);
vector<int> grid((m+1)*(n+1));
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
int k;
fscanf(file,"%d",&k);
grid[indexFor(i,j)] = k;
}
}
int startX,startY,endX,endY;
fscanf(file,"%d",&startX);
fscanf(file,"%d",&startY);
fscanf(file,"%d",&endX);
fscanf(file,"%d",&endY);
queue<int> x,y;
x.push(1);
y.push(1);
vector<int> visited((m+1)*(n+1),0);
vector<int> queued((m+1)*(n+1),0); // <-- THIS IS WHAT I ADDED
vector<vector<int>> path_track((m+1)*(n+1),vector<int>(2,0));
while(x.size()>0) {
int k = x.front(), l = y.front();
x.pop();
y.pop();
visited[indexFor(k,l)]=1;
cout << "\033[2J\033[H";
cout << "queue size: " << x.size()<<endl;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(visited[indexFor(i,j)]==1) cout << "* ";
else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
usleep(10000);
if(k-1>0) {
if(grid[indexFor(k-1,l)] != 1 && visited[indexFor(k-1,l)]!=1&&!queued[indexFor(k-1,l)]) {
x.push(k-1);
y.push(l);
queued[indexFor(x.back(),y.back())] = 1;
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
if((k+1)<=m) {
if(grid[indexFor(k+1,l)] != 1 && visited[indexFor(k+1,l)]!=1&&!queued[indexFor(k+1,l)]) {
x.push(k+1);
y.push(l);
//cout << "Path_track: "<<x.back() << ", " << y.back() << " : " << k << ", " << l <<endl;
path_track[indexFor(x.back(),y.back())] = {k,l};
queued[indexFor(x.back(),y.back())] = 1;
}}
if(l-1>0) {
if(grid[indexFor(k,l-1)] != 1 && visited[indexFor(k,l-1)]!=1&&!queued[indexFor(k,l-1)]) {
x.push(k);
y.push(l-1);
path_track[indexFor(x.back(),y.back())] = {k,l};
queued[indexFor(x.back(),y.back())] = 1;
}}
if(l+1<=n) {
if(grid[indexFor(k,l+1)] != 1 && visited[indexFor(k,l+1)]!=1&&!queued[indexFor(k,l+1)]) {
x.push(k);
y.push(l+1);
queued[indexFor(x.back(),y.back())] = 1;
path_track[indexFor(x.back(),y.back())] = {k,l};
}}
}
cout << "\033[2J\033[H";
vector<vector<int>> path;
/*
for(int i=1;i<=m;i++) {
for(int j =1;j<=m;j++) {
cout << path_track[indexFor(i,j)][0] << "," << path_track[indexFor(i,j)][1]<< " ";
}
cout << endl;
}
*/
path.push_back({endX,endY});
while(endX!=0&&endY!=0) {
int kx = endX, ky = endY;
endX = path_track[indexFor(kx,ky)][0];
endY = path_track[indexFor(kx,ky)][1];
path.push_back({endX,endY});
}
path.pop_back();
if(path[path.size()-1][0] == startX && path[path.size()-1][1] == startY)
{
for(vector<int> l:path) grid[indexFor(l[0],l[1])] = 8;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(grid[indexFor(i,j)]==8) {
cout << "X ";
} else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
} else {
cout << "No path found\n";
for(vector<int> l:path) grid[indexFor(l[0],l[1])] = 8;
for(int i=1;i<=m;i++) {
for(int j =1;j<=n;j++) {
if(grid[indexFor(i,j)]==8) {
cout << "X ";
} else {
if(grid[indexFor(i,j)]==0) {
cout << ". ";
} else {
cout << "# ";
}
}
}
cout << endl;
}
}
//cout<<path_track[indexFor(2,2)][0]<<","<<path_track[indexFor(2,2)][1]<<endl;
return 0;
}