Buttercola: Indeed: reverse String except HTML entity

Buttercola: Indeed: reverse String except HTML entity
Reverse string except for HTML entities, i.e, A HTML entities must be treated as an entire word without reverse.

e.g. "1234€" => "€4321"
"1234&euro" => "orue&4321"
"1234€567" => "765€4321"

Understand the problem:
Since a HTML entity must start with "&" and end with ";"
This problem can be solved in a two-step approach.
Step 1: reverse non-html tokens, and store the result into a list. For the HTML entity, do not reverse but just store into the result. 
Step 2: construct the final result just concatenate the list in a reverse order.

    public String reverseHTML(String s) {

        if (s == null || s.length() <= 1) {

            return s;

        }

         

        List<String> tokens = new ArrayList<>();

        int i = 0;

        int j = 0;

         

        while (j < s.length()) {

            char c = s.charAt(j);

            // Case 1: if c != &

            if (c != '&') {

                j++;

            } else {

                // step 1: reverse substring before &

                if (j != 0) {

                    String token = reverse(s, i, j - 1);

                    tokens.add(token);

                }

                 

                // step 2: put the html entity into the tokens

                StringBuffer sb = new StringBuffer();

                while (j < s.length() && s.charAt(j) != ';') {

                    sb.append(s.charAt(j));

                    j++;

                }

                 

                if (j < s.length()) {

                    sb.append(';');

                    tokens.add(sb.toString());

                    // step 3: update i

                    j++;

                    i = j;

                }

            }

        }

         

        // Reverse the trailing chars

        if (i < j) {

            String token = reverse(s, i, s.length() - 1);

            tokens.add(token);

        }

         

        // Step 2: concatenate the final result

        StringBuffer result = new StringBuffer();

        for (i = tokens.size() - 1; i >= 0; i--) {

            result.append(tokens.get(i));

        }

         

        return result.toString();

    }

     

    private String reverse(String s, int start, int end) {

        StringBuffer sb = new StringBuffer();

         

        while (start <= end) {

            sb.append(s.charAt(end));

            end--;

        }

         

        return sb.toString();

    }

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