Leetcode: Add Binary

本文介绍了如何将两个二进制字符串相加并返回结果,包括实现细节和代码示例。

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

For example,
a = "11"
b = "1"

Return "100".

Use another string, or a stringbuilder to store the result. Start with the last characters of the two strings, and concatenate the adding result at the beginning of the new string. 

public class Solution {
    public String addBinary(String a, String b) {
        if (a == null && b == null) {
            return null;
        }
        
        String res = "";
        int la = a.length();
        int lb = b.length();
        int carry = 0;
        
        for (int i = 0; i < Math.max(la, lb); i++) {
            int ca = 0;
            int cb = 0;
            if (la - 1 - i >= 0) {
                ca = (int) (a.charAt(la - 1 - i) - '0');
            } 
            if (lb - 1 - i >= 0) {
                cb = (int) (b.charAt(lb - 1 - i) - '0');
            }
            
            if (ca + cb + carry == 3) {
                res = "1" + res;;
                carry = 1;
            } else if (ca + cb + carry == 2) {
                res = "0" + res;
                carry = 1;
            } else {
                res = String.valueOf(ca + cb + carry) + res;
                carry = 0;
            }
        }
        
        if (carry == 1) {
            res = "1" + res;
        }
        
        return res;
    }
}
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