給定兩個二進(jìn)制字符串狰域，返回他們的和（用二進(jìn)制表示）甫题。
輸入為非空字符串且只包含數(shù)字 1 和 0赁遗。
示例 1:
輸入: a = "11", b = "1"
輸出: "100"
示例 2:
輸入: a = "1010", b = "1011"
輸出: "10101
代碼
class Solution {
public:
string addBinary(string a, string b) {
string res;
int na = a.size();
int nb = b.size();
int n = max(na, nb);
bool carry = false;
if (na > nb) {
for (int i = 0; i < na - nb; ++i) b.insert(b.begin(), '0');
}
else if (na < nb) {
for (int i = 0; i < nb - na; ++i) a.insert(a.begin(), '0');
}
for (int i = n - 1; i >= 0; --i) {
int tmp = 0;
if (carry) tmp = (a[i] - '0') + (b[i] - '0') + 1;
else tmp = (a[i] - '0') + (b[i] - '0');
if (tmp == 0) {
res.insert(res.begin(), '0');
carry = false;
}
else if (tmp == 1) {
res.insert(res.begin(), '1');
carry = false;
}
else if (tmp == 2) {
res.insert(res.begin(), '0');
carry = true;
}
else if (tmp == 3) {
res.insert(res.begin(), '1');
carry = true;
}
}
if (carry) res.insert(res.begin(), '1');
return res;
}
};
