How to generate unique numbers in php

php method to generate unique numbers: first initialize the variable to 0; then create a new array and randomly generate a number within a certain range and put it into the array; then remove duplicate values ​​in the array; finally Just store the number of the array in the variable count and give the array a new key name.

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PHP encapsulation method to generate a non-repeating random array

/*
* 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 an array before deduplicating them... It is inefficient... I don’t want to use

PHP to efficiently generate m non-duplicate numbers within the n range. Random number (m

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

This algorithm very cleverly takes the position of the random number (the subscript of the array) instead of taking the random number itself. Every time a random number is taken, it is excluded from the value range. The following Only the remaining numbers will be selected at a time, and the selection of random numbers 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 order of its subscript to obtain an array of $num numeric key values ​​arranged in corresponding order.

2. In the second step, start to get 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. 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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