class Ideone {
public static void main (String[] args) {
    String A = "Hello, how are you?";
    String B = "!%$£*, how are you?";
    String C = "Hello, how are ^&%?";
    System.out.println(mergeDiffStrings(A, B, C));
}
 
static String mergeDiffStrings(String a, String b, String c) {
    StringBuilder sb = new StringBuilder(a);
    for (int i = 0; i < a.length(); i++) {
        if (b.charAt(i) != a.charAt(i)) {
            sb.setCharAt(i, b.charAt(i));
        } else if (c.charAt(i) != a.charAt(i)) {
            sb.setCharAt(i, c.charAt(i));
        }
    }
    return sb.toString();
}
}
 

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