Leetcode 43. Multiply Strings

43. Multiply Strings

• Total Accepted: 72584
• Total Submissions: 292967
• Difficulty: Medium

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.

思路：模拟大数相乘，具体见代码。

代码：

class Solution {
public:
    string multiply(string num1, string num2) {
        int i = 0, j;
        //去除头0
        while (i < num1.size() && num1[i] == '0') i++;
        if (i == num1.size()) return "0";
        num1 = num1.substr(i);
        i = 0;
        while (i < num2.size() && num2[i] == '0') i++;
        if (i == num2.size()) return "0";
        num2 = num2.substr(i);
        vector<int> nums(num1.size()+num2.size(),0);
        for (i = num1.size() - 1; i >= 0; i--) {
            for (j = num2.size() - 1; j >= 0; j--) {
                int mutil = (num1[i]-'0')*(num2[j]-'0') + nums[i + j + 1];
                nums[i + j + 1] = mutil % 10;
                nums[i + j] += mutil / 10;//这个可以保证不会溢出
            }
        }
        string res = "";
        j = 0;
        while (nums[j] == 0) j++;
        while (j < nums.size()) res += to_string(nums[j++]);
        return res;
    }
};