/**

public static String decodeString(String s) {

StringBuilder stack = new StringBuilder();

for (char c : s.toCharArray()) {

if (c != ']') {

stack.append(c);

} else {

StringBuilder sb = new StringBuilder();

while (stack.charAt(stack.length() - 1) != '[') {

sb.insert(0, stack.charAt(stack.length() - 1));

stack.setLength(stack.length() - 1);

}

stack.setLength(stack.length() - 1);

int n = 0, t = 1;

while (stack.length() > 0 && Character.isDigit(stack.charAt(stack.length() - 1))) {

n += t * (stack.charAt(stack.length() - 1) - '0');

t *= 10;

stack.setLength(stack.length() - 1);

}

for (int i = 0; i < n; i++) {

for (int j = 0; j < sb.length(); j++) {

stack.append(sb.charAt(j));

}

}

}

}

return stack.toString();

}

// 耗时3ms，思路很直观，且不容易错，面试推荐写法

public String decodeString2(String s) {

StringBuilder sb = new StringBuilder();

for (char c : s.toCharArray()) {

if (c != ']') {

sb.append(c);

} else {

String t = popString(sb);

for (int i = popCount(sb); i > 0; i--) {

sb.append(t);

}

}

}

return sb.toString();

}

private String popString(StringBuilder sb) {

StringBuilder ss = new StringBuilder();

int i = sb.length() - 1;

for ( ; sb.charAt(i) != '['; i--) {

ss.append(sb.charAt(i));

}

sb.setLength(i);

return ss.reverse().toString();

}

private int popCount(StringBuilder sb) {

int i = sb.length() - 1, cnt = 0, t = 1;

for ( ; i >= 0 && Character.isDigit(sb.charAt(i)); i--, t *= 10) {

cnt += t * (sb.charAt(i) - '0');

}

sb.setLength(i + 1);

return cnt;

}