【leetcode】Add Binary

Add Binary 

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

For example,
a = "11"
b = "1"
Return "100".

 

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先补全字符串，从末尾开始加，每次计算当前位和进位即可

 1 class Solution {

 2 public:

 3     char addBit(char a,char b,char &c)

 4     {

 5         if(a==b&&a=='1')

 6         {

 7             char ret;

 8             ret=c;

 9             c='1';

10             return ret;

11         }

12         else if(a==b&&a=='0')

13         {

14             

15             if(c=='0')

16             {

17                 return '0';

18             }

19             else

20             {

21                 c='0';

22                 return '1';

23             }

24         }

25         else

26         {

27             if(c=='1')

28                return '0';

29             else

30                return '1';

31             

32         }

33     }

34     

35     string addBinary(string a, string b) {

36         

37         int na=a.length()-1;

38         int nb=b.length()-1;

39         

40         if(na!=nb)

41         {

42             string tmp(abs(na-nb),'0');

43             if(na>nb)

44                 b=tmp+b;

45             else

46                 a=tmp+a;

47         }

48         

49         int i=a.length()-1;

50         string result(a.length(), '1');

51         char c='0';

52         

53         while(i>=0)

54         {

55             result[i]=addBit(a[i],b[i],c);

56             i--;

57         }

58         if(c=='0')

59         {

60             return result;

61         }

62         else

63         {

64             return '1'+result;

65         }

66     }

67 };