394_Decode_String.java

classSolution {
publicStringdecodeString(Strings) {
if (s == null || s.isEmpty()) {
return"";
 }

Stack<StringBuilder> sbStk = newStack<>();
Stack<Integer> multipliers = newStack<>();
StringBuilderresult = newStringBuilder();
intmultiplier = 0;

for (inti = 0; i < s.length(); i++) {
charc = s.charAt(i);

if (Character.isDigit(c)) {
multiplier = multiplier * 10 + c - '0';
 } elseif (c == '[') {
sbStk.push(result);
multipliers.push(multiplier);

result = newStringBuilder();
multiplier = 0;
 } elseif (c == ']') {
StringBuilderpreviousString = sbStk.pop();
intprevMultiplier = multipliers.pop();

for (intj = 0; j < prevMultiplier; j++) {
previousString.append(result);
 }

result = previousString;
 } else {
result.append(c);
 }
 }

returnresult.toString();
 }
}