LeetCodr 43 字符串相乘

思路

用一个数组记录乘积的结果，最后处理进位。

代码

class Solution {

public:

    string multiply(string num1, string num2) {

        if(num1 == "0" || num2 == "0")  return "0";

        reverse(num1.begin(), num1.end());

        reverse(num2.begin(), num2.end());

        int a[num1.length() + num2.length() + 1] = {0};

        for(int i = 0; i < num1.length(); i++){

            for(int j = 0; j < num2.length(); j++){

                a[i + j] += (num1[i] - '0') * (num2[j] - '0');

            }

        }

        int mod = 0;

        for(int i = 0; i <= num1.length() + num2.length(); i++){

            a[i] += mod;

            mod = a[i] / 10;

            a[i] %= 10;

        }

        int i = num1.length() + num2.length();

        while(!a[i])    i--;

        string ans = "";

        while(i >= 0){

            ans += a[i] + '0';

            i--;

        }

        return ans;

    }

};