Who would win this battle? Shark vs Alligator?

An alligator vs a shark? In coastal SC (maybe elsewhere too), sometimes you will see alligators swimming around in salt water marshes, so lets say the gator came across a shark, who would win? Or Bull sharks have the ability to live in freshwater and saltwater, say a bull shark got into a body of freshwater somehow that also had gators, who would win that battle?