Do keyword search, duplicate keyword search, or do not match

public static Boolean check(List<String> list, String city) {
		for (String s : list) {
			if (s.equals(city)) {
				return true;
			}
		}
		return false;
	}

	public static void main(String[] args) {
		
		List<String> city = new ArrayList<String>();//1,3,7,13
		city.add(" Shanghai ");
		city.add(" Beijing ");
		city.add(" Shenzhen ");
		city.add(" nanjing ");
		 

		List<String> tempList = new ArrayList<String>();
		for (String c : city) {
			StringBuffer str = new StringBuffer();
			str.append(c);
			if (!tempList.contains(c)) {
				tempList.add(c);
			}

			StringBuffer str2 = new StringBuffer();
			for (String s : city) {
				if (str2.length() > 0) {
					str2.append(",").append(s);
				} else {
					str2.append(s);
				}
				String[] split2 = str2.toString().split(",");
				Arrays.sort(split2);
				String data2 = String.join(",", split2);
				if (!tempList.contains(data2) && !check(tempList, data2)) {
					tempList.add(data2);
				} else {
					str2 = new StringBuffer();
				}

				if (!c.equals(s)) {
					if (str.length() > 0) {
						str.append(",").append(s);
					} else {
						str.append(s);
					}
					String[] split = str.toString().split(",");
					Arrays.sort(split);
					String data = String.join(",", split);
					if (!tempList.contains(data) && !check(tempList, data)) {
						tempList.add(data);
					}
				}
			}

			String[] split = str.toString().split(",");
			Arrays.sort(split);
			String data = String.join(",", split);
			if (!tempList.contains(data) && !check(tempList, data)) {
				tempList.add(data);
			}

		}

		tempList.forEach(e -> {
			System.out.println(e);
		});
	}

Shanghai
Beijing
Shanghai , Beijing
Beijing , Shenzhen
Shanghai , Beijing , Shenzhen
Beijing , nanjing , Shenzhen
Shanghai , Beijing , nanjing , Shenzhen
Shenzhen
nanjing , Shenzhen
Shanghai , Shenzhen
nanjing
Shanghai , nanjing
Shanghai , Beijing , nanjing