string的加和乘
1, char to int / int to char
2, 运算的时候,尽量int with int, char with char
3,当char + int,结果还是char:‘1’ + 2 = ‘3’
https://leetcode.com/problems/add-strings/description/
415. Add Strings
class Solution {
public:
string addStrings(string num1, string num2) {
string res = "";
int n1 = num1.size() - 1;
int n2 = num2.size() - 1 ;
int c = 0;
while(n1 >= 0 || n2 >= 0 || c > 0)
{
if(n1 >= 0) c += (num1[n1--] - '0');
if(n2 >= 0) c += (num2[n2--] - '0');
res = char(c % 10 + '0') + res;
c = c / 10;
}
return res;
}
};
- Multiply Strings
https://leetcode.com/problems/multiply-strings/description/
class Solution {
public:
string multiply(string num1, string num2) {
string res(num1.size() + num2.size(), '0');
for(int i = num1.size() - 1; i >= 0; i--)
{
int c = 0;
for(int j = num2.size() - 1; j >= 0; j--)
{
c += res[i + j +1] - '0' + (num2[j] - '0') * (num1[i] - '0');
res[i + j + 1] = char(c % 10 + '0');
c = c / 10;
}
//int cur = res[i] - '0';
//res[i] = char(cur + c + '0');
res[i] += c;
}
int fnot0 = res.find_first_not_of('0');
if(fnot0 != res.npos)
{
res = res.substr(fnot0);
}
return res;
}
};