PHP randomly generates random numbers that are not in a range

Idea: Store the generated random numbers in an array, and then remove duplicate values ​​in the array to generate a certain number of non-repeating random numbers.

In PHP website development, sometimes we need to generate a certain number of non-repeating random numbers within a specified range. How to specifically design this function to generate random numbers? We can store randomly generated numbers into an array, but by removing duplicate values ​​while storing them, a certain number of non-repeating random numbers can be generated.

You can also store the values ​​in the specified range into an array, then use shuffle($array) to disrupt the array, and then intercept a certain number of values. But the latter method will generate a larger array when the specified range of random numbers is too large.

The code for the first approach is given below, and the second approach is simpler.

<?php
/*
* array unique_rand( int $min, int $max, int $num )
* 生成一定数量的不重复随机数，指定的范围内整数的数量必须
* 比要生成的随机数数量大
* $min 和 $max: 指定随机数的范围
* $num: 指定生成数量
*/
function unique_rand($min, $max, $num) {
  $count = 0;
  $return = array();
  while ($count < $num) {
    $return[] = mt_rand($min, $max);
    $return = array_flip(array_flip($return));
    $count = count($return);
  }
  //打乱数组，重新赋予数组新的下标
  shuffle($return);
  return $return;
}

//生成10个1到100范围内的不重复随机数
$arr = unique_rand(1, 100, 10);
echo implode($arr, ",");
?>

Run results: 48,5,19,36,63,72,82,77,46,16
##Supplementary instructions:

1. When generating random numbers, we used the mt_rand() function. This function generates random numbers several times faster on average than rand().

2. When removing duplicate values ​​from the array, the "flip method" is used, which is to use array_flip() to exchange the key and value of the array twice. This approach is much faster than using array_unique() while removing duplicate values ​​from the array.

3. Before returning the array, first use shuffle() to assign a new key name to the array, ensuring that the key name is a consecutive number from 0-n. If you do not perform this step, it may cause the key names to be discontinuous when deleting duplicate values. If you use for to traverse, there will be problems. However, if you use foreach or do not need to traverse, you do not need shuffle.

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