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public class DecodeString {
//https://leetcode.com/problems/decode-string/
class Solution {
public String decodeString(String s) {
Deque numStack = new ArrayDeque();
Deque strStack = new ArrayDeque();
StringBuilder tail = new StringBuilder();
int n = s.length();
for (int i = 0; i < n; i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
int num = c - '0';
while (i + 1 < n && Character.isDigit(s.charAt(i + 1))) {
num = num * 10 + s.charAt(i + 1) - '0';
i++;
}
numStack.push(num);
} else if (c == '[') {
strStack.push(tail.toString());
tail = new StringBuilder();
} else if (c == ']') {
StringBuilder tmp = new StringBuilder(strStack.pop());
int repeatedTimes = numStack.pop();
for (int j = 0; j < repeatedTimes; j++) {
tmp.append(tail);
}
tail = tmp;
} else {
tail.append(c);
}
}
return tail.toString();
}
}
}