使用rand2（）实现rand3（）-yiteyi-C++库

给定一个以相同概率返回0或1的函数rand2（），使用以相同概率返回0、1或2的rand2（）实现rand3（）。尽量减少对rand2（）方法的调用次数。此外，不允许使用任何其他库函数和浮点算法。

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这个想法是使用表达 2*rand2（）+rand2（） .它以相等的概率返回0,1,2,3。为了使它以相同的概率返回0、1、2，我们消除了不希望出现的事件3。以下是上述想法的实施情况——

C++

                         // C++ Program to print 0, 1 or 2 with equal                       
                         // probability                       
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         // Random Function to that returns 0 or 1 with                       
                         // equal probability                       
                         int                                     rand2()                       
                         {                       
                                                 // rand() function will generate odd or even                       
                                                 // number with equal probability. If rand()                       
                                                 // generates odd number, the function will                       
                                                 // return 1 else it will return 0.                       
                                                 return                                     rand                                     () & 1;                       
                         }                       
                                   
                         // Random Function to that returns 0, 1 or 2 with                       
                         // equal probability 1 with 75%                       
                         int                                     rand3()                       
                         {                       
                                                 // returns 0, 1, 2 or 3 with 25% probability                       
                                                 int                                     r = 2 * rand2() + rand2();                       
                                   
                                                 if                                     (r < 3)                       
                                                 return                                     r;                       
                                   
                                                 return                                     rand3();                       
                         }                       
           
                         // Driver code to test above functions                       
                         int                                     main()                       
                         {                       
                                                 // Initialize random number generator                       
                                                 srand                                     (                                     time                                     (NULL));                       
                                   
                                                 for                                     (                                     int                                     i = 0; i < 100; i++)                       
                                                 cout << rand3();                       
                                   
                                                 return                                     0;                       
                         }                       

JAVA

                         // Java Program to print 0, 1 or 2 with equal                       
                         // probability                       
                         import                                     java.util.Random;                       
                         class                                     GFG                       
                         {                       
           
                                                 // Random Function to that returns 0 or 1 with                       
                                                 // equal probability                       
                                                 static                                     int                                     rand2()                       
                                                 {                       
           
                                                 // rand() function will generate odd or even                       
                                                 // number with equal probability. If rand()                       
                                                 // generates odd number, the function will                       
                                                 // return 1 else it will return 0.                       
                                                 Random rand =                                     new                                     Random();                       
                                                 return                                     (rand.nextInt() &                                     1                                     );                       
                                                 }                       
           
                                                 // Random Function to that returns 0, 1 or 2 with                       
                                                 // equal probability 1 with 75%                       
                                                 static                                     int                                     rand3()                       
                                                 {                       
           
                                                 // returns 0, 1, 2 or 3 with 25% probability                       
                                                 int                                     r =                                     2                                     * rand2() + rand2();                       
           
                                                 if                                     (r <                                     3                                     )                       
                                                 return                                     r;                       
                                                 return                                     rand3();                       
                                                 }                       
           
                                                 // Driver code                       
                                                 public                                     static                                     void                                     main(String[] args) {                       
                                                 for                                     (                                     int                                     i =                                     0                                     ; i <                                     100                                     ; i++)                       
                                                 System.out.print(rand3());                       
                                                 }                       
                         }                       
                         // This code is contributed by divyesh072019.                       

Python3

                         # Python3 Program to print 0, 1 or 2 with equal                       
                         # Probability                       
           
                         import                                     random                       
                         # Random Function to that returns 0 or 1 with                       
                         # equal probability                       
           
                         def                                     rand2():                       
           
                                                 # randint(0,100) function will generate odd or even                       
                                                 # number [1,100] with equal probability. If rand()                       
                                                 # generates odd number, the function will                       
                                                 # return 1 else it will return 0                       
                                                 tmp                                     =                                     random.randint(                                     1                                     ,                                     100                                     )                       
                                                 return                                     tmp                                     %                                     2                       
                                   
                         # Random Function to that returns 0, 1 or 2 with                       
                         # equal probability 1 with 75%                       
                         def                                     rand3():                       
                                   
                                                 # returns 0, 1, 2 or 3 with 25% probability                       
                                                 r                                     =                                     2                                     *                                     rand2()                                     +                                     rand2()                       
                                                 if                                     r<                                     3                                     :                       
                                                 return                                     r                       
                                                 return                                     rand3()                       
                                   
                         # Driver code to test above functions                       
                         if                                     __name__                                     =                                     =                                     '__main__'                                     :                       
                                                 for                                     i                                     in                                     range                                     (                                     100                                     ):                       
                                                 print                                     (rand3(),end                                     =                                     "")                       
                                   
                         #This code is contributed by sahilshelangia                       

C#

                         // C# Program to print 0, 1 or 2 with equal                       
                         // probability                       
                         using                                     System;                       
                         class                                     GFG                       
                         {                       
           
                                                 // Random Function to that returns 0 or 1 with                       
                                                 // equal probability                       
                                                 static                                     int                                     rand2()                       
                                                 {                       
           
                                                 // rand() function will generate odd or even                       
                                                 // number with equal probability. If rand()                       
                                                 // generates odd number, the function will                       
                                                 // return 1 else it will return 0.                       
                                                 Random rand =                                     new                                     Random();                       
                                                 return                                     (rand.Next() & 1);                       
                                                 }                       
           
                                                 // Random Function to that returns 0, 1 or 2 with                       
                                                 // equal probability 1 with 75%                       
                                                 static                                     int                                     rand3()                       
                                                 {                       
           
                                                 // returns 0, 1, 2 or 3 with 25% probability                       
                                                 int                                     r = 2 * rand2() + rand2();                       
           
                                                 if                                     (r < 3)                       
                                                 return                                     r;                       
                                                 return                                     rand3();                       
                                                 }                       
           
                                                 // Driver code                       
                                                 static                                     void                                     Main()                       
                                                 {                       
                                                 for                                     (                                     int                                     i = 0; i < 100; i++)                       
                                                 Console.Write(rand3());                       
                                                 }                       
                         }                       
           
                         // This code is contributed by divyeshrabadiya07.                       

PHP

                         <?php                       
                         // PHP Program to print 0, 1 or                       
                         // 2 with equal probability                       
           
                         // Random Function to that                       
                         // returns 0 or 1 with                       
                         // equal probability                       
                         function                                     rand2()                       
                         {                       
                                                 // rand() function will generate                       
                                                 // odd or even number with equal                       
                                                 // probability. If rand() generates                       
                                                 // odd number, the function will                       
                                                 // return 1 else it will return 0.                       
                                                 return                                     rand() & 1;                       
                         }                       
           
                         // Random Function to that                       
                         // returns 0, 1 or 2 with                       
                         // equal probability 1 with 75%                       
                         function                                     rand3()                       
                         {                       
                                                 // returns 0, 1, 2 or 3                       
                                                 // with 25% probability                       
                                                 $r                                     = 2 * rand2() + rand2();                       
                                   
                                                 if                                     (                                     $r                                     < 3)                       
                                                 return                                     $r                                     ;                       
                                   
                                                 return                                     rand3();                       
                         }                       
           
                         // Driver Code                       
           
                         // Initialize random                       
                         // number generator                       
                         srand(time(NULL));                       
           
                         for                                     (                                     $i                                     = 0;                                     $i                                     < 100;                                     $i                                     ++)                       
                                                 echo                                     rand3();                       
           
                         // This code is contributed by aj_36                       
                         ?>                       

输出：

2111011101112002111002020210112022022022211100100121202021102100010200121121210122011022111020

另一个解决方案—— 如果x=rand2（）和y=rand2（），x+y将以25%的概率返回0和2，以50%的概率返回1。为了使1的概率等于0和2的概率，即25%，我们消除了一个导致x+y=1的意外事件，即（x=1，y=0）或（x=0，y=1）。

int rand3(){    int x, y;    do {        x = rand2();        y = rand2();    } while (x == 0 && y == 1);    return x + y;}

请注意，上述解决方案每次运行时都会产生不同的结果。本文由 阿迪蒂亚·戈尔 .如果你喜欢GeekSforgek，并想贡献自己的力量，你也可以使用贡献极客。组织或者把你的文章寄到contribute@geeksforgeeks.org.看到你的文章出现在Geeksforgeks主页上，并帮助其他极客。如果您发现任何不正确的地方，或者您想分享有关上述主题的更多信息，请写下评论。

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