Java solution: public static String appendAndDelete(String s, String t, int k) {

int stringSLength = s.length();
int stringTLength = t.length();
int difference = Math.abs(stringSLength - stringTLength);

if(t.charAt(0) != s.charAt(0)){
    if(stringSLength + stringTLength <= k){
        return "Yes";
    }
    else{
        return "No";
    }
}
else{

    if(difference == 0 && !s.equals(t)){
        for(int i = 0; i < stringSLength; i++){
            if (s.charAt(stringSLength - 1 - i) != t.charAt(stringTLength - 1 - i)) {
                difference = i;
                break;
            }
        }
    }

    if(difference <= k){
        if(difference % 2 != 0 && k % 2 == 0){
            return "No";
        }

        return "Yes";
    }
    else{
        return "No";

    }
}

}