67. Add Binary

• Difficulty: Easy

• Topics: Math, String

• Similar Questions:

  • Add Two Numbers

  • Multiply Strings

  • Plus One

  • Add to Array-Form of Integer

Problem:

Given two binary strings, return their sum (also a binary string).

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

Solutions:

class Solution {
public:
    string addBinary(string a, string b) {
        string ret;
        int carry = 0;
        int indexA = a.length() - 1;
        int indexB = b.length() - 1;

        while (indexA >= 0 || indexB >= 0) {
            int digitA = 0;
            int digitB = 0;
            if (indexA >= 0) {
                digitA = a[indexA--] - '0';
            }

            if (indexB >= 0) {
                digitB = b[indexB--] - '0';
            }

            int val = carry + digitA + digitB;
            ret.push_back('0' + val%2);
            carry = val/2;
        }

        if (carry == 1) ret.push_back('1');
        reverse(ret.begin(), ret.end());
        return ret;
    }
};