zzzz-'s blog

By zzzz-, history, 2 years ago, In English

We all know what a permutation is. So, I remember a good problem from school. Let P be a permutation of 1, 2, 3, .... n. We define the function f(P) as the number of positions where P[i] = i (also known as fixed points I think). What is the expect value of f :)

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