题目

地址

https://leetcode.com/problems/add-binary/description/

内容

Given two binary strings a and b, return their sum as a binary string.

Example 1:

Input: a = “11”, b = “1”
Output: “100”

Example 2:

Input: a = “1010”, b = “1011”
Output: “10101”

Constraints:

• 1 <= a.length, b.length <= 10⁴
• a and b consist only of ‘0’ or ‘1’ characters.
• Each string does not contain leading zeros except for the zero itself.

解题

这题是考察大数（二进制模式）的求和。由于题中要求二进制字符长度上限比较大，所以不能将数据转成二进制直接计算，我们只能从后向前逐位相加，并记录进位。
在计算时，我们将字符“1”转成数字1，然后就可以使用取模和除法来计算是否需要进位等。
唯一的边界就是最后两个字符串相加完，需要进位的场景。

#include <string>
using namespace std;

class Solution {
public:
    string addBinary(string a, string b) {
        int carry = 0;
        string result;
        for (int i = a.size() - 1, j = b.size() - 1; i >= 0 || j >= 0; i--, j--) {
            int sum = (i >= 0 ? a[i] - '0' : 0) + (j >= 0 ? b[j] - '0' : 0) + carry;
            carry = sum / 2;
            result.insert(result.begin(), sum % 2 + '0');
        }
        if (carry > 0) {
            result.insert(result.begin(), carry + '0');
        }
        return result;
    }
};

代码地址