320: Generalized Abbreviation

Write a function to generate the generalized abbreviations of a word.

Example: Given word = "word", return the following list (order does not matter):

["word", "1ord", "w1rd", "wo1d", "wor1", "2rd", "w2d", "wo2", >"1o1d", "1or1", "w1r1", "1o2", "2r1", "3d", "w3", "4"]

public List<String> generateAbbreviations(String word) {
    List<String> res = new ArrayList<>();
    DFS(res, new StringBuilder(), word.toCharArray(), 0, 0);
    return res;
}

public void DFS(List<String> res, StringBuilder sb, char[] c, int i, int num) {
    int len = sb.length();  
    if(i == c.length) {
        if(num != 0) sb.append(num);
        res.add(sb.toString());
    } else {
        DFS(res, sb, c, i + 1, num + 1);               // abbr c[i]

        if(num != 0) sb.append(num);                   // not abbr c[i]
        DFS(res, sb.append(c[i]), c, i + 1, 0);        
    }
    sb.setLength(len); 
}

https://leetcode.com/discuss/76783/java-14ms-beats-100%25

Group: remove parentheses:

https://leetcode.com/discuss/72208/easiest-9ms-java-solution

add operators:

https://leetcode.com/discuss/75308/java-simple-and-fast-solution-beats-96-56%25