private static void solve(Grid grid, List<Grid> solutions) {
// Return if there is already more than two solution
if (solutions.size() >= 2) {
return;
}
// Find first empty cell
int loc = grid.findEmptyCell();
// If no empty cells are found,a solution is found
if (loc < 0) {
solutions.add(grid.clone());
return;
}
// Try each of the 9 digits in this empty cell
for (int n = 1; n < 10; n++) {
if (grid.set(loc, n)) {
// With this cell set,work on the next cell
solve(grid, solutions);
// Clear the cell so that it can be filled with another digit
grid.clear(loc);
}
}
}
