Given two numbers represented as strings, return multiplication of the numbers as a string.
Note: The numbers can be arbitrarily large and are non-negative.
题意：字符串的乘法。
思路：摹拟竖乘的思路，跟大数计算1样，先将字符串颠倒
class Solution {
public:
string multiply(string num1, string num2) {
reverse(num1.begin(), num1.end());
reverse(num2.begin(), num2.end());
int len1 = num1.size(), len2 = num2.size();
string ans(len1+len2+1, '0');
int tmp = 0;
for (int i = 0; i < len1; i++) {
int cur = num1[i] - '0';
tmp = 0;
for (int j = 0; j < len2; j++) {
int a = tmp + cur * (num2[j]-'0') + (ans[i+j]-'0');
tmp = a / 10;
ans[i+j] = a % 10 + '0';
}
int idx = len2;
while (tmp != 0) {
int a = tmp + (ans[i+idx]-'0');
tmp = a / 10;
ans[i+idx] = a % 10 + '0';
idx++;
}
}
while (!ans.empty() && ans.back() == '0')
ans.pop_back();
if (ans.empty()) return "0";
reverse(ans.begin(), ans.end());
return ans;
}
};