[leetcode] 415. Add Strings(大數相加)

Add Strings

描述

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note
1.The length of both num1 and num2 is < 5100.
2.Both num1 and num2 contains only digits 0-9.
3.Both num1 and num2 does not contain any leading zero.
4.You must not use any built-in BigInteger library or convert the inputs to integer directly.

我的代碼

class Solution {
public:
    string addStrings(string num1, string num2) {
        int len1 = num1.length();
        int len2 = num2.length();
        if (len1==0 || len2==0) return "0";

        int len = (len1 > len2) ? len1 + 1 : len2 + 1;
        int* rlt = new int[len];
        memset(rlt, 0, sizeof(int)*len);

        int ind = len-1;
        int carry = 0;
        int i = len1 - 1;
        while (i >= 0)
        {
            int val = num1[i--] - '0' + carry;
            rlt[ind--] = val % 10;
            carry = val / 10;
        }
        rlt[ind] = carry;

        ind = len - 1;
        carry = 0;
        int j = len2 - 1;
        while (j >= 0)
        {
            int val = rlt[ind] + num2[j--] - '0' + carry;
            rlt[ind--] = val % 10;
            carry = val / 10;
        }
        //出現第二個數字的長度小於第一個數字的長度的情況，要處理進位carry向前的傳遞!!
        while (ind >= 0)
        {
            int val = rlt[ind] + carry;
            rlt[ind--] = val % 10;
            carry = val / 10;
        }
        //轉化成string
        string s = "";
        int strInd = (rlt[0]==0)?1:0;
        for (; strInd < len; strInd++)
        {
            s += (rlt[strInd] + '0');
        }
        return s;
    }
};