Method backtrack

LetterTilePossibilities.java:2–18

(String tiles,String output,HashSet<String> set, Boolean visited[])

class Solution {
    public static void backtrack(String tiles,String output,HashSet<String> set, Boolean visited[]){
    //  Base Case
    if(output.length()>0)
    {
        if(set.contains(output))
            return;
        set.add(output);
    }
        for(int i=0;i<tiles.length();i++)
        {
            if(visited[i]) continue;
            visited[i] = true;
            backtrack(tiles,output+tiles.charAt(i),set,visited);
            visited[i] = false;
        }
        return;
    }
    public int numTilePossibilities(String tiles) {
        HashSet<String> set = new HashSet<String>();
        Boolean visited[] = new Boolean[tiles.length()];