题目：

题解：

class Solution {public String multiply(String num1, String num2) {if (num1.equals("0") || num2.equals("0")) {return "0";}int m = num1.length(), n = num2.length();int[] ansArr = new int[m + n];for (int i = m - 1; i >= 0; i--) {int x = num1.charAt(i) - '0';for (int j = n - 1; j >= 0; j--) {int y = num2.charAt(j) - '0';ansArr[i + j + 1] += x * y;}}for (int i = m + n - 1; i > 0; i--) {ansArr[i - 1] += ansArr[i] / 10;ansArr[i] %= 10;}int index = ansArr[0] == 0 ? 1 : 0;StringBuffer ans = new StringBuffer();while (index < m + n) {ans.append(ansArr[index]);index++;}return ans.toString();}
}