这个题其实很简单的。。思路快的话2分钟就做出来了。。比较难一点的版本。。
toss a fair coin, what is the expected number of tosses to get m consecutive heads?
继续更难一些（这个没遇到过的估计要翻资料才能做出来了）
toss a fair coin n times, what is the probability to get at least m (m<=n) consecutive heads?
继续更难一些（这个没遇到过的估计要翻资料才能做出来了）
toss a fair coin n times, what is the probability to get at least m (m<=n) consecutive heads?
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