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LeetCode: 43. Multiply Strings

Posted on Edited on In , Valine: 
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class Solution {
public:
    string multiply(string num1, string num2) {
        int len = num1.size() + num2.size();
        vector<int> nums(len, 0);
        for(int i=num1.size()-1;i>=0;--i)
            for(int j=num2.size()-1;j>=0;--j)
                nums[i+j+1]+=(num1[i]-'0')*(num2[j]-'0');
        for(int i=len-1;i>0;--i)
        {
            nums[i-1]+=nums[i]/10;
            nums[i]=nums[i]%10;
        }

        string ret;
        int idx=0;
        while(nums[idx]==0 && idx!=len-1)
            ++idx;
        while(idx<len)
            ret+=(nums[idx++]+'0');
        return ret;
    }
};