ЯсноПонятно24

import java.util.stream.Collectors;

public class App {
    public static String nrzi(String signal) {
        if (signal.isEmpty()) {
            return "";
        }
        
        char prev = signal.charAt(0);
        return signal.substring(1)
                .chars()
                .mapToObj(c -> c == '|' ? '0' : c == prev ? '0' : '1')
                .peek(c -> prev = c)
                .collect(StringBuilder::new, StringBuilder::append, StringBuilder::append)
                .toString();
    }

    public static void main(String[] args) {
        String signal1 = "_|¯|____|¯|__|¯¯¯";
        System.out.println(nrzi(signal1)); // "011000110100"

        String signal2 = "|¯|___|¯¯¯¯¯|___|¯|_|¯";
        System.out.println(nrzi(signal2)); // "110010000100111"

        String signal3 = "¯|___|¯¯¯¯¯|___|¯|_|¯";
        System.out.println(nrzi(signal3)); // "010010000100111"

        String signal4 = "";
        System.out.println(nrzi(signal4)); // ""

        String signal5 = "|";
        System.out.println(nrzi(signal5)); // ""
    }
}