How to generate non-repeating random numbers in php

How to generate non-repeating random numbers in php: first assign a value to each number in the array in order of its subscript; then start to take random numbers in the range of "[i, $num-1]"; finally, in Just perform alternating operations on the unchanged key-value pairs.

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PHP efficiently generates a non-repeating random number

PHP generates a non-repeating random array encapsulation method

/*
* array unique_rand( int $min, int $max, int $num )
* 生成一定数量的不重复随机数
* $min 和 $max: 指定随机数的范围
* $num: 指定生成数量
*/
function unique_rand($min, $max, $num) {
//初始化变量为0
$count = 0;
//建一个新数组
$return = array();
while ($count < $num) {
//在一定范围内随机生成一个数放入数组中
$return[] = mt_rand($min, $max);
//去除数组中的重复值用了“翻翻法”，就是用array_flip()把数组的key和value交换两次。这种做法比用 array_unique() 快得多。
$return = array_flip(array_flip($return));
//将数组的数量存入变量count中
$count = count($return);
}
//为数组赋予新的键名
shuffle($return);
return $return;
}

This method obtains random numbers each time and stores them in the array before deduplicating...it is inefficient. ..I don’t want to use

PHP to efficiently generate m non-repeating random numbers in the n range (m<=n)

Note: It is also mentioned in the book "Programming Pearls", the title For "How to efficiently generate m non-repeating random numbers in the range of n (m<=n)"

This algorithm is very clever in taking the position of the random number (the subscript of the array), instead of taking the random number itself , every time a random number is obtained, it will be excluded from the value range, and next time it will only be taken from the remaining numbers. The random number selection can be completed in one traversal, which is quite efficient.

function rand_num($num='200'){
for($i=0;$i<$num;$i++){
$n[$i] = $i;
}
for($i=0;$i<$num;$i++){
$rand = mt_rand($i,$num-1);
//数组  随机数交换下标
if($n[$i] == $i){
$n[$i] = $n[$rand];
$n[$rand] = $i;
}
}
}

1. The first step is to assign a value to each number in the array in the order of its subscript, and obtain an array of $num numeric key values ​​arranged in corresponding order.

2. In the second step, start taking the random number $rand in the range [i, $num-1], and use the obtained random number $rand as the subscript corresponding to the current position key i in the array Value $rand, replace the value corresponding to the subscript of key $rand in the array with i. This is actually a cross-exchange of array key values. The meaning is to exclude the generated random number from the value range [i,$num-1], and next time it will take the value from the remaining numbers [i 1,num-1].

3. In the third step, in order to avoid repeated values, only perform alternating operations on the unchanged key-value pairs, that is, perform alternating operations on the positions where the original array is arranged sequentially (key == value).

4. End.

Sequential array partial exchange process

As shown above, obtain 10 random number partial examples.

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