[LeetCode]Multiply Strings

public class Solution {
public String multiply(String num1, String num2) {
int length1 = num1.length();
int length2 = num2.length();
int[] record = new int[length1 + length2];
for (int i = length1 - 1; i >= 0; i--) {
for (int j = length2 - 1; j >= 0; j--) {
int tmp = (num1.charAt(i) - '0') * (num2.charAt(j) - '0');
int p2 = i + j + 1;
int p1 = p2 - 1;
tmp += record[p2];
record[p2] = tmp % 10;
record[p1] += (tmp) / 10;
}
}
StringBuffer result = new StringBuffer("");
for (int i = record.length - 1; i >= 0; i--) {
result.insert(0, String.valueOf(record[i]));
}
String r = String.valueOf(result);
while(r.length() > 1 && r.startsWith("0")) {
r = r.substring(1);
}
return r;
}
}