415. Add Strings

最新推荐文章于 2020-09-23 07:53:04 发布

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本文介绍了一种不使用内置大整数库或直接转换为整数的两个非负整数字符串相加的方法。通过从后向前逐位计算并处理进位，确保了结果的正确性。

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

Note:

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

这个题就是把两个字符串加起来，我自己归类到“部分开放字符串问题”，因为目标字符串的长度不确定，所以可以从后向前计算。详情请参见482. License Key Formatting

class Solution {
public:
    string addStrings(string num1, string num2) {
        if (num1.length() ==0) return num2;
        if (num2.length() == 0) return num1;
        int index1 = num1.length() - 1;
        int index2 = num2.length() - 1;
        string result;
        int carry = 0;
        while (index1 >= 0 || index2 >= 0) {
            int d1 = index1 >= 0 ? num1[index1--] - '0' : 0;
            int d2 = index2 >= 0 ? num2[index2--] - '0' : 0;
            int sum = d1 + d2 + carry;
            result += ((sum % 10) + '0');
            carry = sum / 10;
          
        }
        if (carry != 0) result += (carry + '0');
        return string(result.rbegin(), result.rend());
    }
};