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`3`	`3`	`包括Reject sampling 和 Fisher-Yates Shuffle 以及蓄水池算法`
`4`	`4`
	`5`	`+蓄水池算法`
	`6`	`+`
	`7`	`+计算复杂度高,空间复杂度低,核心逻辑,选择第i个数的概率 1/i \* (1 - 1/(i+1)) \* (1 - 1/(i+2)) \* (1 - 1/N) = 1/N,比较适合流数据处理,也可生成k/N 个随机数`
	`8`	`+`
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	`10`	`+`
`5`	`11`	`### 470.Implement Rand10() Using Rand7()`
`6`	`12`
`7`	`13`	`使用7个数字表达出更多个数字,构造两位7进制,(rand7() - 1) \* 7 + rand7() - 1,可以取得0-48之间的数字。如得到0-39之间的数字,使用(num % 10 + 1)等概率映射出1-10. 如得到40-48之间的数字,重新选择...直到选择到0-39之间的数字`

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