Description
Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.
Note: You must not use any built-in BigInteger library or convert the inputs to integer directly.
Example
Example 1:
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| Input: num1 = "2", num2 = "3"
Output: "6"
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Example 2:
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| Input: num1 = "123", num2 = "456"
Output: "56088"
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Constraints:
- 1 <= num1.length, num2.length <= 200
- num1 and num2 consist of digits only.
- Both num1 and num2 do not contain any leading zero, except the number 0 itself.
Solution
Time Complexity:
- Space Complexity:
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| class Solution {
public String multiply(String num1, String num2) {
if (num1.equals("0") || num2.equals("0")) return "0";
int[] product = new int[num1.length() + num2.length()];
for (int i = num1.length() - 1; i >= 0; i--){
for (int j = num2.length() - 1; j >= 0; j--){
int a = num1.charAt(i) - '0';
int b = num2.charAt(j) - '0';
product[i + j + 1] += a * b;
}
}
int carry = 0;
for (int i = product.length - 1; i >= 0; i--){
int temp = (product[i] + carry) % 10;
carry = (product[i] + carry) / 10;
product[i] = temp;
}
StringBuilder res = new StringBuilder();
for (int num: product)
res.append(num);
while(res.length() > 0 && res.charAt(0) == '0') res.deleteCharAt(0);
return res.length() == 0 ? "0" : res.toString();
}
}
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