PHP不重复随机数的生成方法

原理很简单，先写一个函数，生成0-z这36个字符中的一个。每次调用 getOptions() 方法生成一个字符，它们的存储如下：array[0] = 0, array[1] = 1, ……, array[35] = z。

Array ( 
	[0] => 0 
	[1] => 1 
	[2] => 2 
	[3] => 3 
	[4] => 4 
	[5] => 5 
	[6] => 6 
	[7] => 7 
	[8] => 8 
	[9] => 9 
	[10] => a 
	[11] => b 
	[12] => c 
	[13] => d 
	[14] => e 
	[15] => f 
	[16] => g 
	[17] => h 
	[18] => i 
	[19] => j 
	[20] => k 
	[21] => l 
	[22] => m 
	[23] => n 
	[24] => o 
	[25] => p 
	[26] => q 
	[27] => r 
	[28] => s 
	[29] => t 
	[30] => u 
	[31] => v 
	[32] => w 
	[33] => x 
	[34] => y 
	[35] => z 
)

然后在0-35之间随机生成一个数作为索引，其实就是在上面数组中随机取出一个数，作为变量 $result 中的第一个字符。这个随机索引随后会被赋值成数组最后一个，它将不会参与下一轮的随机选取。