bit AND 연산 구현

private int bitAndOperator(List<Integer> nums) {
List<String> bits = new ArrayList<>();
int maxLength = 0;

for (Integer num : nums) {
String e = Integer.toBinaryString(num);
if (maxLength < e.length()) {
maxLength = e.length();
}
bits.add(e);
}
List<String> padBits = new ArrayList<>();
for (String bit : bits) {
padBits.add(pad(bit, maxLength));
}
System.out.println(padBits);

Map<Integer, List<String>> posPerBits = new LinkedHashMap<>();
for (int i = 0; i < maxLength; i++) {
posPerBits.put(i, getAndValue(padBits, i));
}
String res = "";
for (Map.Entry<Integer, List<String>> entry : posPerBits.entrySet()) {
if (isAllPositive(entry.getValue())) {
res += "1";
} else {
res += "0";
}
}

return Integer.parseInt(res, 2);
}

private boolean isAllPositive(List<String> value) {
for (String s : value) {
if (s.equals("0")) {
return false;
}
}
return true;
}

private List<String> getAndValue(List<String> padBits, int i) {
List<String> res = new ArrayList<>();
for (String padBit : padBits) {
res.add(String.valueOf(padBit.charAt(i)));
}
return res;
}

private String pad(String input, int maxLength) {
int padLen = maxLength - input.length();
if (padLen > 0) {
for (int i = 0; i < padLen; i++) {
input = ("0" + input);
}
}
return input;
}