private Set<String> generateOneCharFreSubseq(Collection<String> segments){
		
		Map<String, Integer> fileAccessTimes = new HashMap<String, Integer>();
		Set<String> oneFileFreSubseqs = new HashSet<String>();
		
		// 统计每个文件出现的次数
		for(String segment: segments){
			String[] files = segment.split("\\|");
			for(String file: files){
				// 统计每个文件出现的次数
				Integer count = fileAccessTimes.get(file) == null ? 0 : fileAccessTimes.get(file);
				fileAccessTimes.put(file, count + 1);
			}
		}
		
		// 过滤掉出现次数小于minSupport的子序列
		for(Map.Entry<String, Integer> entry: fileAccessTimes.entrySet()){
			if(entry.getValue() >= minSupport){
				oneFileFreSubseqs.add(entry.getKey());
			}
		}
		
		return oneFileFreSubseqs;
	}