最近在刷 leetcode 的时候遇到了一道算法题（缺失的第一个正数），发现正好可以应用到最近的一个小功能里，功能很简单，就是类似于谷歌浏览器下载重复文件会在重复的文件后面加序号 “(1)”，用这个算法刚好可以实现。
/**
* <p> Handle Repeat File Name Utils </p>
*
* @author mask
* @since 2023/10/27 15:56
*/
public class FileRepeatNameUtils {
public static void main(String[] args) {
System.out.println(handleRepeatFileName("D:\UserFiles\桌面", "域名.txt"));
}
/**
* <p> 处理重复文件名 </p>
*
* 例子：
* <pre>
* 1. 有后缀文件
* a.txt -> a (1).txt
*
* 2. 没有后缀文件
* aaa -> aaa (1)
*
* 3. 该路径不存在该重复文件
* aaa -> aaa
* </pre>
*
* @param basePath 待处理的文件路径 {@code D:\UserFiles\桌面}
* @param fileName 文件名 {@code a.txt}
* @return 如果存在重复文件则返回 {@code a (1).txt}
*/
public static String handleRepeatFileName(String basePath, String fileName) {
String fullFileName = basePath + File.separator + fileName;
File file = new File(fullFileName);
if (!file.exists()) {
return fileName;
}
int pointIndex = fileName.lastIndexOf(".");
String finalPrefixFileName = fileName;
if (pointIndex > 0) {
finalPrefixFileName = fileName.substring(0, pointIndex);
}
String format = String.format("(?<=%s) \((\d+)\).*", finalPrefixFileName);
Pattern pattern = Pattern.compile(format);
File baseFile = new File(basePath);
String[] list = baseFile.list();
if (ObjectUtils.isEmpty(list)) return fileName;
List<Integer> numList = new ArrayList<>();
for (String name : list) {
Matcher matcher = pattern.matcher(name);
if (matcher.find()) {
int order = Integer.parseInt(matcher.group(1));
numList.add(order);
}
}
int finalOrder = 1;
if (!numList.isEmpty()) {
finalOrder = firstMissingPositive(numList);
}
StringBuilder finalFileName = new StringBuilder(fileName);
finalFileName.insert(pointIndex > 0 ? pointIndex : fileName.length(), " (" + (finalOrder) + ")");
return finalFileName.toString();
}
/**
* 算法来自: <a href="https://leetcode.cn/submissions/detail/478439446/">缺失的第一个正数</a>
*/
private static int firstMissingPositive(List<Integer> numList) {
int[] nums = new int[numList.size()];
for (int i = 0; i < nums.length; i++) {
nums[i] = numList.get(i);
}
int length = nums.length;
for (int i = 0; i < length; i++) {
while (nums[i] >= 1 && nums[i] <= length && nums[nums[i] - 1] != nums[i]) {
swap(nums, i, nums[i] - 1);
}
}
for (int i = 0; i < nums.length; i++) {
if (nums[i] != i + 1) return i + 1;
}
return length + 1;
}
private static void swap(int[] nums, int i, int j) {
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
}
