标签：nta tip turn first sel substr npos inpu and
Given two non-negative integers num1 and num2 represented 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:
num1 and num2 is < 110.num1 and num2 contain only digits 0-9.num1 and num2 do not contain any leading zero, except the number 0 itself.my code:
class Solution {
public:
string multiply(string num1, string num2) {
int len1 = num1.length();
int len2 = num2.length();
if (len1 == 1 && num1[0] == ‘0‘ ||
len2 == 1 && num2[0] == ‘0‘)
return "0";
vector<string> v;
int incidental;
int multiply;
for (int i = len2 - 1; i >= 0; --i) {
incidental = 0;
int n2 = num2[i] - ‘0‘;
string tem = "";
for (int k = (len2 - 1) - i; k > 0; --k) {
tem += ‘0‘;
}
for (int j = len1 - 1; j >= 0; --j) {
int n1 = num1[j] - ‘0‘;
multiply = n1 * n2 + incidental;
incidental = multiply / 10;
tem += to_string(multiply%10);
}
if (incidental != 0)
tem += to_string(incidental);
v.push_back(tem);
}
int max_length = v.back().size();
string ans = "";
int flag;
incidental = 0;
for (int i = 0; i < max_length; ++i) {
flag = 0;
for (int j = 0; j < v.size(); ++j) {
if (i < v[j].size()) {
int tage = v[j][i] - ‘0‘;
flag += tage;
}
}
flag += incidental;
incidental = flag / 10;
ans = to_string(flag % 10) + ans;
}
if (incidental != 0)
ans = to_string(incidental) + ans;
return ans;
}
};
Runtime: 24 ms, faster than 14.44% of C++ online submissions for Multiply Strings.
efficient code:
class Solution {
public:
string multiply(string num1, string num2) {
string sum(num1.size() + num2.size(), ‘0‘);
for (int i = num1.size() - 1; 0 <= i; --i) {
int carry = 0;
for (int j = num2.size() - 1; 0 <= j; --j) {
int tmp = (sum[i + j + 1] - ‘0‘) + (num1[i] - ‘0‘) * (num2[j] - ‘0‘) + carry;
sum[i + j + 1] = tmp % 10 + ‘0‘;
carry = tmp / 10;
}
sum[i] += carry;
}
size_t startpos = sum.find_first_not_of("0");
if (string::npos != startpos) {
return sum.substr(startpos);
}
return "0";
}
};
Runtime: 4 ms, faster than 100.00% of C++ online submissions for Multiply Strings.
标签：nta tip turn first sel substr npos inpu and
原文地址：https://www.cnblogs.com/ruruozhenhao/p/9800318.html
