RandomNumberGenerator

public class RandomNumberGenerator {

/**
* 这是典型的随机洗牌算法。 流程是从备选数组中选择一个放入目标数组中，将选取的数组从备选数组移除（放至最后，并缩小选择区域） 算法时间复杂度O(n)
*
* @return 随机8为不重复数组
*/
public static String generateNumber() {
String no = "";
// 初始化备选数组
int[] defaultNums = new int[10];
for (int i = 0; i < defaultNums.length; i++) {
defaultNums[i] = i;
}

Random random = new Random();
int[] nums = new int[LENGTH];
// 默认数组中可以选择的部分长度
int canBeUsed = 10;
// 填充目标数组
for (int i = 0; i < nums.length; i++) {
// 将随机选取的数字存入目标数组
int index = random.nextInt(canBeUsed);
nums[i] = defaultNums[index];
// 将已用过的数字扔到备选数组最后，并减小可选区域
swap(index, canBeUsed - 1, defaultNums);
canBeUsed--;
}
if (nums.length > 0) {
for (int i = 0; i < nums.length; i++) {
no += nums[i];
}
}

return no;
}

private static final int LENGTH = 8;

private static void swap(int i, int j, int[] nums) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}

public static String generateNumber2() {
String no = "";
int num[] = new int[8];
int c = 0;
for (int i = 0; i < 8; i++) {
num[i] = new Random().nextInt(10);
c = num[i];
for (int j = 0; j < i; j++) {
if (num[j] == c) {
i--;
break;
}
}
}
if (num.length > 0) {
for (int i = 0; i < num.length; i++) {
no += num[i];
}
}
return no;
}

public static void main(String[] args) {
Map<String, String> mpa = new HashMap<String, String>();
for (int i = 0; i < 600; i++) {
// System.out.println(generateNumber());
String idString = generateNumber2();
mpa.put(idString, idString);
System.out.println(idString);
}
System.out.println(mpa.size());
}
}