題目來源
將兩個數(shù)字字符串相加，返回結(jié)果字符串，我原來想著轉(zhuǎn)換為整型，然后進(jìn)行加法，然后再轉(zhuǎn)為字符串。代碼如下：

class Solution {
public:
    string addStrings(string num1, string num2) {
        int n1 = num1.size(), n2 = num2.size();
        long long v1 = 0, v2 = 0;
        for (int i=0; i<n1; i++) {
            v1 = v1 * 10 + (num1[i] - '0');
        }
        for (int i=0; i<n2; i++) {
            v2 = v2 * 10 + (num2[i] - '0');
        }
        return to_string(v1 + v2);
    }
};

但是發(fā)現(xiàn)字符串長度可以達(dá)到5000+位，直接gg，轉(zhuǎn)換為整型的方法顯然行不通了。然后得一個一個加，代碼如下：

class Solution {
public:
    string addStrings(string num1, string num2) {
        int n1 = num1.size(), n2 = num2.size();
        int n = max(n1, n2);
        string res = "";
        bool carry = false;
        for (int i=1; i<=n; i++) {
            int tmp1 = n1 >= i ? num1[n1-i] - '0' : 0;
            int tmp2 = n2 >= i ? num2[n2-i] - '0' : 0;
            int tmp = tmp1 + tmp2;
            if (carry) 
                tmp++;
            res = to_string(tmp % 10) + res;
            carry = tmp / 10;
        }
        if (carry)
            res = '1' + res;
        return res;
    }
};