复杂度分析:时间复杂度O(n);空间复杂度O(1)
import java.util.*;
import java.io.*;
class Main {
static final Scanner cin = new Scanner(System.in);
public static void main(String[] args) {
String s = cin.next();
int n = s.length();
StringBuilder builder = new StringBuilder();
for (int i = 0; i < n; i ++) {
char ch = s.charAt(i);
if (ch >= '0' && ch <= '9') {
int num = ch - '0';
for (int j = 2; j <= num; j ++) {
builder.append("" + s.charAt(i - 1));
}
}else {
builder.append("" + s.charAt(i));
}
}
System.out.println(builder.toString());
}
}