Given two binary strings, return their sum (also a binary string). For example, a = “11” b = “1” Return “100”. ~~~ public class Solution { public String addBinary(String a, String b) { //int alen=a.length; //int blen=b.length; //int alen=a.size-1; //int alen=a.length-1; int alen=a.length()-1; int blen=b.length()-1; int c=0; char[] achar=a.toCharArray(); char[] bchar=b.toCharArray(); //int rlen=Math.max(achar.length,bchar.length+1); //int rlen=Math.max(achar.length,bchar.length+2); int rlen=Math.max(achar.length,bchar.length)+2; char[] rchar=new char[rlen]; int k=0; while(true){ if(alen<0 && blen<0 && c==0){ break; } int al=0; int bl=0; //if(alen>0){ if(alen>=0){ al=achar[alen]-'0'; } //if(blen>0){ if(blen>=0){ //a=achar[blen]-'0'; bl=bchar[blen]-'0'; } if(al+bl+c>1){ rchar[k]=(char)('0'+al+bl+c-2); c=1; }else{ rchar[k]=(char)('0'+al+bl+c); c=0; } k++; alen--; blen--; } return new StringBuffer(new String(rchar, 0, k)).reverse().toString(); } } ~~~