leetcode 43. Multiply Strings(高精度乘法)

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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.
Converting the input string to integer is NOT allowed.
You should NOT use internal library such as BigInteger.

高精度乘法。需要注意的是char表示的数字和int对应的数字之间的转化。

class Solution {

public:

    string multiply(string num1, string num2) {

        int l1=num1.length(),l2=num2.length();

        if(l1==||l2==){

            string ans="";

            return ans;

        }

        string ans(l1+l2,'');

        for(int i=l1-;i>=;i--){

            int add=;

            for(int j=l2-;j>=;j--){

                int t=(ans[i+j+]-'')+(num1[i]-'')*(num2[j]-'')+add;

                ans[i+j+]=t%+'';

                add=t/;

            }

            ans[i]=add+'';

        }

        size_t s0 = ans.find_first_not_of('');

        if(s0!=string::npos){

            return ans.substr(s0);

        }

        return "";

    }

};