题解 | #字符串排列#

    public ArrayList<String> getPermutation(String A) {
        // write code here
        ArrayList<String> res = new ArrayList<>();
        if(A ==  null || A.length() == 0) return res;
        char[] chs = A.toCharArray();

        dfs(chs, 0 , res);
        Collections.sort(res);
        Collections.reverse(res);
        return res;
    }

    public void dfs(char[] chs, int start, ArrayList<String> res){
        if(start == chs.length){
            res.add(new String(chs));
        }

        for(int i = start ; i < chs.length; i ++){
            swap(chs, i , start);
            dfs(chs, start + 1, res);
            swap(chs, i , start);
        }
    }

    public void swap(char[] arr , int i , int j ){
        char tem = arr[i];
        arr[i] = arr[j];
        arr[j] = tem;
    }