LeetCode(67):Add Binary

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

For example,

a = "11"

b = "1"

Return "100".

题意：本题意思很明了，给定2个String，分别存储了用二进制表示的数，实现二进制的加法。

思路：从右向左逐位相加，注意进位即可。

代码：

public String addBinary(String a, String b) {
        
      int  flag = 0;
      int aIndex = a.length() - 1;
      int bIndex = b.length() - 1;
      String c="";
      while(aIndex>=0&&bIndex>=0){
          int num = a.charAt(aIndex) - '0' + (b.charAt(bIndex) - '0') + flag;
          flag = num/2;
          num %= 2;
          c = String.valueOf((char)(num+'0'))+ c;
          aIndex --;
          bIndex --;
      }
      while(aIndex >= 0){
          int num = a.charAt(aIndex) - '0' + flag;
          flag = num /2;
          num %= 2;
          c =String.valueOf((char)(num+'0')) + c;
          aIndex--;
      }
      while(bIndex >= 0){
          int num = b.charAt(bIndex) - '0' + flag;
          flag = num /2;
          num %= 2;
          c =String.valueOf((char)(num+'0')) + c;
          bIndex--;
      }
      if(flag>0){
           c = String.valueOf(flag) + c;
      }
    return c;    
    }