Given two non-negative integers num1 and num2represented as strings, return the product of num1 and num2, also represented as a string.
Example 1:
Input: num1 = "2", num2 = "3" Output: "6"Example 2:
Input: num1 = "123", num2 = "456" Output: "56088"Note:
The length of both num1 and num2 is < 110.Both num1 and num2 contain only digits 0-9.Both num1 and num2 do not contain any leading zero, except the number 0 itself.You must not use any built-in BigInteger library or convert the inputs to integer directly.原答案讲解
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(); }