Find all rectangles from two dimensions array which contain 0

    /**
int[][] arr = {
{ 0,   0,   1,  0},
{ 0,   0,   1,  1},
{ 1,   1,   0,  0},
{ 0,   1,   0,  0},
};
List list = findRectangle(arr);
for(Coord c: list){
c.print();
}

x1 = 0
y1 = 0
x2 = 1
y2 = 1

x1 = 3
y1 = 0
x2 = 3
y2 = 0

x1 = 0
y1 = 3
x2 = 0
y2 = 3

x1 = 2
y1 = 2
x2 = 3
y2 = 3
*/
public static List findRectangle(int[][] arr){
List list = new ArrayList<>();
if(arr != null && arr.length > 0){
int ncol = arr.length;
int nrow = arr[0].length;
for(int c = 0; c < ncol; c++){
for(int r = 0; r < nrow; r++){
if(arr[c][r] == 0){

int rn = 0;
int rr = r;
while(rr < nrow && arr[c][rr] == 0){
rn ++;
rr++;
}

int cn = 0;
int cc = c;
while(cc < ncol && arr[cc][r] == 0){
cn++;
cc++;
}

Coord coord = new Coord();
coord.x1 = r;
coord.y1 = c;
coord.x2 = r + rn - 1;
coord.y2 = c + cn - 1;

// flip all 0 to 1 in the current rectangle
for(int y = coord.y1; y <= coord.y2; y++){
for(int x = coord.x1; x <= coord.x2; x++){
arr[y][x] = 1;
}
}
}
}
}
}
return list;
}