Given two binary strings, return their sum (also a binary string).
For example,
a = "11"
b = "1"
Return "100".
思路：
从最低位加到最高位，当前位相加结果是%2，进位是/2，记得处理每一次的进位和最后一次的进位，最后反向输出字符。
Java:
public class AddBinary {
public String addBinary(String a, String b) {
StringBuilder result = new StringBuilder();
int pointerA = a.length()-1;
int pointerB = b.length()-1;
int carry = 0;
while(pointerA>=0 || pointerB>=0){
int sum = carry;
if(pointerA>=0){
sum += (a.charAt(pointerA)-‘0‘);
pointerA--;
}
if(pointerB>=0){
sum += (b.charAt(pointerB)-‘0‘);
pointerB--;
}
result.append(sum%2);
carry = sum/2;
}
if(carry!=0){
result.append(‘1‘);
}
return result.reverse().toString();
}
}
C++ 1:
class Solution {
public:
string addBinary(string a, string b) {
string res;
size_t res_len = max(a.length(), b.length()) ;
size_t carry = 0;
for (int i = 0; i < res_len; ++i) {
const size_t a_bit_i = i < a.length() ? a[a.length() - 1 - i] - ‘0‘ : 0;
const size_t b_bit_i = i < b.length() ? b[b.length() - 1 - i] - ‘0‘ : 0;
size_t sum = carry + a_bit_i + b_bit_i;
carry = sum / 2;
sum %= 2;
res.push_back(‘0‘ + sum);
}
if (carry) {
res.push_back(‘0‘ + carry);
}
reverse(res.begin(), res.end());
return res;
}
};
C++ 2:
class Solution {
public:
string addBinary(string a, string b) {
string res = "";
int m = a.size() - 1, n = b.size() - 1, carry = 0;
while (m >= 0 || n >= 0) {
int p = m >= 0 ? a[m--] - ‘0‘ : 0;
int q = n >= 0 ? b[n--] - ‘0‘ : 0;
int sum = p + q + carry;
res = to_string(sum % 2) + res;
carry = sum / 2;
}
return carry == 1 ? "1" + res : res;
}
};
Python:
class Solution:
# @param a, a string
# @param b, a string
# @return a string
def addBinary(self, a, b):
result, carry, val = "", 0, 0
for i in xrange(max(len(a), len(b))):
val = carry
if i < len(a):
val += int(a[-(i + 1)])
if i < len(b):
val += int(b[-(i + 1)])
carry, val = val / 2, val % 2
result += str(val)
if carry:
result += str(carry)
return result[::-1]
if __name__ == ‘__main__‘:
result = Solution().addBinary(‘11‘, ‘1‘)
print result
后续Followup：
如果不是二进制相加，而是十六进制相加呢？只要把算法中的除2和余2换成16，并添加相应的十六进制字母就行了。
如果是带小数的
