Pixel distance flood-fill - c++

Question

Problem statement:
Input is a rectangular bitmap like this:
0001
0011
0110
The task is to find for each black (0) "pixel", the distance to the
closest white (1) "pixel". So, the output to the above should be:
3 2 1 0
2 1 0 0
1 0 0 1
I have a working solution to the problem, which I posted here, asking for advice on performance improvement. In effort to implement #Jerry Coffin's solution (suggested in an answer to the question) I wrote the following code, which, unfortunately, produces garbage output. For example, the output for the input from the problem statement is
1 1 1 0
11 11 0 0
110 0 0 1
Why doesn't the code work?
#include <iostream>
#include <string>
#include <queue>
using namespace std;
const unsigned short MAX = 200;
typedef unsigned short coordinate;
typedef pair<coordinate,coordinate> coordinates;
//Converts char[] to unsigned int
coordinate atou(char* s) {
coordinate x = 0;
while(*s) x = x*10 + *(s++) - '0';
return x;
}
//Returns array of immediate neighbours of pixel of coordinates c
coordinates* neighbours_of(coordinates c) {
static coordinates neighbours[7];
coordinate i = c.first;
coordinate j = c.second;
neighbours[0] = coordinates(i+1,j);
neighbours[1] = coordinates(i+1,j+1);
neighbours[2] = coordinates(i,j+1);
neighbours[3] = coordinates(i-1,j+1);
neighbours[4] = coordinates(i-1,j);
neighbours[5] = coordinates(i-1,j-1);
neighbours[6] = coordinates(i,j-1);
neighbours[7] = coordinates(i+1,j-1);
return neighbours;
}
int main() {
unsigned short test_cases, wave_number, initial_wave_size;
coordinate m, n, i, j;
int A[MAX][MAX];
coordinates* directions;
string row;
queue<coordinates> ones;
queue<coordinates> wave;
coordinates current_coordinates;
bool found_some_zero;
cin >> test_cases;
while(test_cases--) {
//Input
cin >> n;
cin >> m;
for(i = 0; i < n; i++) {
cin >> row;
for(j = 0; j < m; j++) {
if(row[j] == '1') {
A[i][j] = -1;
ones.push(coordinates(i,j));
} else A[i][j] = atou(&row[j]);
}
}
//Initilization
wave = ones;
wave_number = 1;
found_some_zero = true;
//Filling algorithm
while(found_some_zero) {
found_some_zero = false;
initial_wave_size = wave.size();
while(initial_wave_size--) {
current_coordinates = wave.front();
directions = neighbours_of(current_coordinates);
//Try all directions
for(int k = 0; k < 8; k++) {
i = directions[k].first;
j = directions[k].second;
//If on screen and not yet visited
if(i < n && j < m && A[i][j] == 0) {
//Mark visited
A[i][j] = wave_number;
//(i,j) will be part the next wave
wave.push(coordinates(i,j));
found_some_zero = true;
}
}
wave.pop();
}
wave_number++;
}
//-1 to 0
while(!ones.empty()) {
current_coordinates = ones.front();
i = current_coordinates.first;
j = current_coordinates.second;
A[i][j] = 0;
ones.pop();
}
//Output
for(i = 0; i < n; i++) {
for(j = 0; j < m; j++)
cout << A[i][j] << " ";
cout << endl;
}
}
return 0;
}

Answer 1

The input loop is buggy. Instead of
if(row[j] == '1') {
A[i][j] = -1;
ones.push(coordinates(i,j));
} else A[i][j] = atou(&row[j]);
you need to do
if(row[j] == '1') {
A[i][j] = -1;
ones.push(coordinates(i,j));
} else A[i][j] = 0;
Also, neighbors[7] should be neighbors[8], and you should use only the four cardinal directions if you want to match the specified output exactly.