Multiply Strings
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.
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Example 1:
Input: num1 = "2", num2 = "3"
Output: "6"
Example 2:
Input: num1 = "123", num2 = "456"
Output: "56088"
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
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class Solution {
public:
string multiply(string num1, string num2) {
int len1 = num1.size();
int len2 = num2.size();
string ans;
for (int i = 0; i < len1 + 1 + len2; i++) {
ans.push_back('0');
}
for (int j = len2 - 1; j >= 0; j--) {
int carry = 0;
for (int i = len1 - 1; i >= 0; i--) {
int tmp = (num1[i] - '0') * (num2[j] - '0');
int round = len1 - 1 - i + len2 - 1 - j;
int val = tmp + carry;
val += (ans[round] - '0');
ans[len2 - 1 - j + len1 - 1 -i] = val % 10 + '0';
carry = val >= 10 ? val / 10 : 0;
}
if (carry != 0) {
ans[len1 + len2 - 1 - j] = carry + '0';
}
}
reverse(ans.begin(), ans.end());
int nextZeroIndex;
for (nextZeroIndex = 0; nextZeroIndex < ans.size() - 1; nextZeroIndex++) {
if (ans[nextZeroIndex] != '0') {
break;
}
}
return ans.substr(nextZeroIndex);
}
};
