LeetCode in Net

67. Add Binary

Easy

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.

Solution

public class Solution {
    public string AddBinary(string a, string b) {
        var sb = new System.Text.StringBuilder();
        int i = a.Length - 1; 
        int j = b.Length - 1; 
        int carry = 0;
        while (i >= 0 || j >= 0 || carry > 0) {
            int sum = carry;
            if (i >= 0) {
                sum += a[i--] - '0';
            }
            if (j >= 0) {
                sum += b[j--] - '0';
            }
            sb.Insert(0, (char)('0' + (sum % 2)));
            carry = sum / 2;
        }
        return sb.ToString();
    }
}

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