台服活動介紹：賓果 2、幸運的睏寶寶石（20210205）

剛用類似組合數學的角度計算滿盤要花的寶石個數
約要花 728.775 個寶石
但我也不太清楚實際情形 XD

python 程式碼如下：

arr = [1,1,10,9,10,9,20,17,5,4,
    10,7,5,3,20,9,20,7,5,2,
    20,9,100,47,50,21,10,3,50,11,
    100,19,100,17,20,1,50,9,100,7,
    100,9,50,1,100,3,1000,9,2000,3]

def c(a,b):
    ret = 1
    for i in range(b):
        ret *= (a-i)
    for i in range(b):
        ret /= i+1
    return ret

ans = 0

for i in range(25):
    a = arr[i*2]
    b = arr[i*2+1]
    tmp = 0
    sta = 1
    while(sta + b - 1 <= a):
        tmp += sta * c(a-sta,b-1)
        sta = sta + 1
    ans += tmp / c(a,b)

print(ans)