public bool Equals(FlatMap <Key, Value> that)
{
return(keys.SequenceEqual(that.keys) && values.SequenceEqual(that.values));
}
public SparseArray(int size, T @default = default)
{
this.size = size;
this.@default = @default;
this.items = new FlatMap <int, T>((i, j) => i - j);
}