php method to implement non-repeating random numbers: first initialize the variable to 0; then create a new array; then randomly generate a number within a certain range and put it into the array, and remove duplicate values ​​in the array; finally Just give the array a new key name.

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PHP generates a packaging method for 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 n ranges Non-repeating random numbers within (m<=n)

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<=n)"

This algorithm is very clever in taking the position of the random number (<span style="color:#ff6820; background-color:rgb(252,245,239)">The subscript of the array </span>), instead of taking the random number itself. Every time a random number is obtained, it will be excluded from the value range. Next time, only the remaining By selecting from numbers, 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 order of its subscript to obtain a $num number. Key values ​​correspond to an array arranged in 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 is used as the value of the key i corresponding to the subscript at the current position in the array $rand, and the key in the array The value of $rand corresponding to the subscript is replaced with i, which is actually the array key value cross-exchange. The meaning is to exclude the generated random number from the value range [ i,$num-1], next time It will take the value among 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, arrange them sequentially in the original array (key == value) positions are alternately operated.

4. The end.

Arrange the array in orderPartial exchange process

As shown above, obtain 10 random number partial test examples.

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