equals method
Implementation
bool equals(Object? o) {
if (o == null) {
return false;
}
if (o.runtimeType != SudokuState) {
return false;
}
var other = o as SudokuState;
if (this == other) {
return true;
}
var equal = true;
for (var i = 0; i < board.length; i++) {
for (var j = 0; j < board.length; j++) {
if (board[i][j] != other.board[i][j]) {
equal = false;
}
}
}
return equal;
}