According to "five stars for literary critics," what previous work influenced shakespeare's hamlet?

Literary Influences
Many sources of influence can be seen in Shakespeare's literary According to Amanda Mabillard--in her online article--"Introduction to Hamlet," she notes that Seneca, who was known as the father or revenged tragedies, was a heavy influence on Shakespeare. Shakespeare's exposure to Seneca's work may have pushed him to write a similar sub-genre as seen in Hamlet. 
Additionally, Hamlet's plot is similar to several other revenge tragedies including Kyd Thomas' The Spanish Tragedy, his also alleged Ur-Hamlet, and Saxo Grammaticus's Geste Danorum as noted by the British Library's article, "Hamlet-Shakespeare in Quartos;" however, Grammaticus's Geste Danorum is the most similar to Hamlet's plot due to the fact that they both contain the exact same elements but in different forms (Mabillard). In addition, Shakespeare, being a playwright, gave fuller depth to the story and its characters. 
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