[LeetCode4]Add Binary

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

For example,
a = "11"
b = "1"

Return "100".

Analysis:

The idea is simple. Use carry and current digit number. notice the calcuate order.

Java

public String addBinary(String a, String b) {        int carry = 0;        StringBuffer result = new StringBuffer();        for(int i=a.length()-1,j=b.length()-1;i>=0||j>=0;i--,j--){        int a1 = i>=0? (a.charAt(i)-'0'):0;        int b1 = j>=0? (b.charAt(j)-'0'):0;        int digit = (a1+b1+carry)%2;        carry = (a1+b1+carry)/2;        result.insert(0, digit);        }        if(carry==1)        result.insert(0, '1');        return result.toString();    }

c++

string addBinary(string a, string b) {        string result;    reverse(a.begin(),a.end());    reverse(b.begin(),b.end());    int maxL = a.size()>b.size() ? a.size() : b.size();    int carry = 0;    for(int i=0; i<maxL; i++){        int la = i<a.size()? a[i]-'0':0;        int lb = i<b.size()? b[i]-'0':0;        int sum = (la+lb+carry)%2;        carry = (la+lb+carry)/2;        result.insert(result.begin(),sum+'0');    }    if(carry == 1)        result.insert(result.begin(),'1');    return result;    }

ps:

如果把二进制换成16进制，怎么做。 facebook面试题

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