题目
Given a function rand7 which generates a uniform random integer in the range 1 to 7, write a function rand10 which generates a uniform random integer in the range 1 to 10.
Do NOT use system’s Math.random().
解题思路
随机两次，通过这个两个数可以生产1-49直接的随机数，如果在1-40内，%10+1为结果，如果不在，继续随机
代码
class Solution:
def rand10(self):
"""
:rtype: int
"""
while True:
r1, r2 = rand7(), rand7()
t = r1 + (r2 - 1) * 7
if t <= 40:
return t % 10 + 1
