Birthday Paradox n balls are thrown into m bins: event each bin receives 1 balls m与[ m(m-1)…(m-n+1) Pr[8]= [n→m mn i(-)Birthday Paradox Pr[ℰ] = [n] 1−1 [m] [n] → [m] = m(m − 1)⋯(m − n + 1) mn = n−1 ∏ i=0 (1 − i m ) n balls are thrown into m bins: event ℰ: each bin receives ≤ 1 balls