Remove All Duplicate Lines in a File

题目：
.Given a text file, remove all the duplicate lines, maintaining the order such that the first occurrences of the lines stay in the same order.

解题思路：
这道题就是运用set+双指针的方法来解决。

代码：

public class RemoveAllDuplicateLinesinaFile {

    /*    *    google -> onsite -> google -> onsite -> wanted    *                                            fast    *                        slow    *    the output should maintain the relative order in the    *    original string    * */
    public String remove(String s){
        if(s == null || s.length() == 0){
            return "";
        }
        String[] strings = s.split("->");
        int slow = 0;
        int fast = 0;
        int len = strings.length;
        Set<String> set = new HashSet<>();
        while(fast <= len - 1){
            if(set.contains(strings[fast])){
                fast++;
            }
            else{
                set.add(strings[fast]);
                strings[slow++] = strings[fast++];
            }
        }
        StringBuilder sb = new StringBuilder();
        // the last index should be slow        int i = 0;
        while(i <= slow - 1){
            sb.append(strings[i]);
            if(i != slow - 1){
                sb.append("->");
            }
            i++;
        }
        return sb.toString();
    }

    public static void main(String[] args){
        RemoveAllDuplicateLinesinaFile removeAllDuplicateLinesinaFile = new RemoveAllDuplicateLinesinaFile();
        String s = "google->onsite->google->onsite->wanted";
        String rst = removeAllDuplicateLinesinaFile.remove(s);
        System.out.println(rst);
    }

}