Reverse_Prefix_of_Word.java

class Solution {
    public String reversePrefix(String word, char ch) {
        int index = word.indexOf(ch);
        if (index == -1) {
            return word;
        }
        StringBuilder sb = new StringBuilder(word.substring(0, index + 1));
        return sb.reverse().append(word.substring(index + 1)).toString();
    }
}