Parrot fortune-telling routine

I used to know that one of the hundreds of surnames on the ground is the same as the card you took, and he can 100% calculate your surname, but! What I saw today is that two words are the same! The algorithm is definitely different, and the brain can't turn around. My calculation should have a success rate of 50%, but the fortune teller is accurate! Ask experts for answers, thank you, don't answer if you don't understand,

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