class Solution {

public String multiply(String num1, String num2) {

int m = num1.length(), n = num2.length();

int[] pos = new int[m + n];

for (int i = m - 1; i >= 0; i--) {

for (int j = n - 1; j >= 0; j--) {

int mul = (num1.charAt(i) - '0') * (num2.charAt(j) - '0');

int p1 = i + j, p2 = i + j + 1;

int sum = mul + pos[p2];

pos[p1] += sum / 10;

pos[p2] = (sum) % 10;

}

}

StringBuilder sb = new StringBuilder();

for (int p : pos) {

if (!(sb.length() == 0 && p == 0)) {

sb.append(p);

}

}

return sb.length() == 0 ? "0" : sb.toString();

}

}