ReversePrefix.java

// Approach 1 : Insert at start and concatenate
class Solution {
    public String reversePrefix(String word, char ch) {
        StringBuilder res = new StringBuilder();
        for(int i = 0; i < word.length(); i++){
            char cur = word.charAt(i);
            res.insert(0, cur);

            if(cur == ch){
                res.append(word.substring(i + 1, word.length()));
                return res.toString();
            }
        }
        return word;
    }
}

// Approach 2 : Swap the characters
class Solution {
    public String reversePrefix(String word, char ch) {
        char res[] = word.toCharArray();
        int L = 0;
        for(int R = 0; R < word.length(); R++){
            char cur = res[R];

            if(cur == ch){
                while(L < R){
                    char t = res[R];
                    res[R] = res[L];
                    res[L] = t;
                    L++;
                    R--;    
                }
                return new String(res);
            }
        }
        return word;
    }
}