等概率生成 1 到 7 的整数
原文:https://www . geesforgeks . org/generate-integer-从 1 到 7 等概率/
给定一个以相等概率返回 1 到 5 之间的整数的函数 foo()，只使用 foo()编写一个以相等概率返回 1 到 7 之间的整数的函数。尽量减少对 foo()方法的调用次数。此外，不允许使用任何其他库函数，也不允许使用浮点运算。 解: 我们知道 foo()返回 1 到 5 的整数。我们如何保证 1 到 7 的整数以相等的概率出现？ 如果我们以某种方式以相等的概率生成从 1 到 7 的倍数(如 7、14、21、…)的整数，我们可以使用 7 的模除，然后加上 1，以相等的概率得到从 1 到 7 的数字。 我们可以使用以下表达式以相等的概率生成 1 到 21。
5*foo() + foo() -5
让我们看看如何使用上面的表达式。 1。对于第一个 foo()的每个值，第二个 foo()的值可以有 5 种可能的组合。总共有 25 种可能的组合。 2。上式返回的值的范围是 1 到 25，每个整数恰好出现一次。 3。如果方程的值小于 22，返回模除以 7，然后加 1。否则，再次递归调用该方法。因此，返回每个整数的概率变成 1/7。 下面的程序显示，表达式将从 1 到 25 的每个整数精确地返回一次。
C++
#include <stdio.h>
int main()
{
int first, second;
for ( first=1; first<=5; ++first )
for ( second=1; second<=5; ++second )
printf ("%d \n", 5*first + second - 5);
return 0;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java code to demonstrate
// expression returns each integer
// from 1 to 25 exactly once
class GFG {
public static void main(String[] args)
{
int first, second;
for ( first=1; first<=5; ++first )
for ( second=1; second<=5; ++second )
System.out.printf ("%d \n", 5*first + second - 5);
}
}
// This code is contributed by
// Smitha Dinesh Semwal
Python 3
# Python3 code to demonstrate
# expression returns each integer
# from 1 to 25 exactly once
if name == '__main__':
for first in range(1, 6):
for second in range(1, 6):
print(5 * first + second - 5)
# This code is contributed by Smitha Dinesh Semwal.
C
// C# code to demonstrate expression returns
// each integer from 1 to 25 exactly once
using System;
class GFG {
public static void Main()
{
int first, second;
for ( first = 1; first <= 5; ++first )
for ( second = 1; second <= 5; ++second )
Console.WriteLine ( 5*first + second - 5);
}
}
// This code is contributed by Sam007.
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to Generate integer
// from 1 to 7 with equal probability
$first;
$second;
for ( $first = 1; $first <= 5; ++$first )
for ( $second = 1; $second <= 5; ++$second )
echo 5 * $first + $second - 5, "\n";
// This code is contributed by ajit.
?>
java 描述语言
<script>
// Javascript Program to demonstrate
// expression returns each integer
// from 1 to 25 exactly once
// Driver Code
let first, second;
for ( first=1; first<=5; ++first )
for ( second=1; second<=5; ++second ) {
document.write( 5*first + second - 5);
document.write("<br />");
}
</script>
输出:
1
2
.
.
24
25
时间复杂度: O(1)
辅助空间: O(1)
下面的程序描述了我们如何使用 foo()以相等的概率返回 1 到 7。
C++
// C++ program to Generate integer from
// 1 to 5 with equal probability
#include <stdio.h>
// given method that returns 1 to 5 with equal probability
int foo()
{
// some code here
}
int my_rand() // returns 1 to 7 with equal probability
{
int i;
i = 5*foo() + foo() - 5;
if (i < 22)
return i%7 + 1;
return my_rand();
}
// Driver code
int main()
{
printf ("%d ", my_rand());
return 0;
}
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to Generate integer from
// 1 to 5 with equal probability
class GfG
{
// given method that returns 1 to 5 with equal probability
static int foo()
{
// some code here
return 0;
}
// returns 1 to 7 with equal probability
public static int my_rand()
{
int i;
i = 5*foo() + foo() - 5;
if (i < 22)
return i%7 + 1;
return my_rand();
}
// Driver code
public static void main (String[] args) {
System.out.println(my_rand());
}
}
Python 3
# Python3 program to Generate integer
# from 1 to 5 with equal probability
# given method that returns 1 to 5
# with equal probability
def foo():
# some code here
return 0;
# returns 1 to 7 with equal probability
def my_rand():
i = 0;
i = (5 * foo()) + (foo() - 5);
if (i < 22):
if(i < 0):
return (i % 7 - 7) + 1;
else:
return (i % 7) + 1;
return my_rand();
# Driver code
if __name__ == '__main__':
print(my_rand());
# This code contributed by PrinciRaj1992
C
// C# program to Generate integer from
// 1 to 5 with equal probability
using System;
class GfG
{
// given method that returns 1 to 5 with equal probability
static int foo()
{
// some code here
return 0;
}
// returns 1 to 7 with equal probability
public static int my_rand()
{
int i;
i = 5*foo() + foo() - 5;
if (i < 22)
return i%7 + 1;
return my_rand();
}
// Driver code
public static void Main () {
Console.Write(my_rand()+"\n");
}
}
服务器端编程语言（Professional Hypertext Preprocessor 的缩写）
<?php
// PHP program to Generate integer from
// 1 to 5 with equal probability
// given method that returns 1 to 5
// with equal probability
function foo()
{
// some code here
}
// returns 1 to 7 with equal probability
function my_rand()
{
$i;
$i = 5 * foo() + foo() - 5;
if ($i < 22)
return $i % 7 + 1;
return my_rand();
}
// Driver code
echo my_rand();
// This code is contributed by Tushil.
?>
java 描述语言
<script>
// Javascript program to Generate integer from
// 1 to 5 with equal probability
// given method that returns 1 to 5 with equal probability
function foo()
{
// some code here
return 0;
}
// returns 1 to 7 with equal probability
function my_rand()
{
let i;
i = 5*foo() + foo() - 5;
if (i < 22)
return i%7 + 1;
return my_rand();
}
// Driver code
document.write(my_rand());
// This code is contributed by rag2127
</script>
输出:
-4
时间复杂度: O(1)
辅助空间: O(1)
本文由aashis Barnwal编辑，GeeksforGeeks 团队审核。如果你发现任何不正确的地方，请写评论，或者你想分享更多关于上面讨论的话题的信息
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