[Swift]LeetCode470. 用 Rand7() 实现 Rand10() | Implement Ran

发布时间：2020-12-14 05:04:56 所属栏目：百科来源：网络整理

导读：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() .? Example 1: Input: 1Output

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().?

Example 1:

Input: 1
Output: [7]

Example 2:

Input: 2
Output: [8,4]

Example 3:

Input: 3
Output: [8,1,10]?

Note:

rand7?is predefined.
Each testcase has one argument:?n,the number of times that?rand10is called.?

Follow up:

What is the?expected value?for the number of calls to?rand7()?function?
Could you minimize the number of calls to?rand7()?

已有方法?rand7?可生成 1 到 7 范围内的均匀随机整数，试写一个方法?rand10?生成 1 到 10 范围内的均匀随机整数。

不要使用系统的?Math.random()?方法。?

示例 1:

输入: 1
输出: [7]

示例 2:

输入: 2
输出: [8,4]

示例 3:

输入: 3
输出: [8,10]?

提示:

rand7?已定义。
传入参数:?n?表示?rand10?的调用次数。?

进阶:

rand7()调用次数的?期望值?是多少??
你能否尽量少调用?rand7()??

Runtime:?44 ms

Memory Usage:?5.9 MB

 1 /**
 2  * The rand7() API is already defined in the parent class SolBase.
 3  * func rand7() -> Int = {}
 4  * @return a random integer in the range 1 to 7
 5  */
 6 class Solution : SolBase {
 7     func rand10() -> Int {
 8         while(true)
 9         {
10             var a:Int = rand7()
11             var b:Int = rand7()
12             var num:Int = (a - 1) * 7 + b
13             if num <= 40 {return num % 10 + 1}
14             a = num - 40
15             b = rand7()
16             num = (a - 1) * 7 + b
17             if num <= 60 {return num % 10 + 1}
18             a = num - 60
19             b = rand7()
20             num = (a - 1) * 7 + b
21             if num <= 20 {return num % 10 + 1}
22         }
23     }
24 }

 1 /**
 2  * The rand7() API is already defined in the parent class SolBase.
 3  * func rand7() -> Int = {}
 4  * @return a random integer in the range 1 to 7
 5  */
 6 class Solution : SolBase {
 7     func rand10() -> Int {
 8         var a,b,no: Int?
 9         repeat {
10             a = rand7() - 1
11             b = rand7() - 1
12             no = 7 * a! + b!
13         } while (no! > 39)
14         
15         return (no! % 10) + 1
16     }
17 }

?48 ms

 1 /**
 2  * The rand7() API is already defined in the parent class SolBase.
 3  * func rand7() -> Int = {}
 4  * @return a random integer in the range 1 to 7
 5  */
 6 class Solution : SolBase {
 7     func rand10() -> Int {
 8         var num:Int = (rand7() - 1) * 7 + rand7()
 9         return (num <= 40) ? (num % 10 + 1) : rand10()        
10     }
11 }

（编辑：李大同）

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[Swift]LeetCode470. 用 Rand7() 实现 Rand10() | Implement Ran

44ms