is validation and train set should be all different files?
Validation set is basically to understand how your model is behaving in terms of over-fitting, and under-fitting, and also to find the best set of hyper-parameters for your algorithm. If you use some parts of the same training data on your validation set, then this hypothesis would not be justified. 
Hence, it is suggested to split your data set into train/validation/test set without any overlapping of the data.