第30题 Add Binary

public class Solution {
    public String addBinary(String a, String b) {
        int lengthA = a.length();
        int lengthB = b.length();
        int minLength, maxLength;
        String minStr, maxStr;
        if(lengthA<=lengthB){
            minLength = lengthA;
            minStr = a;
            maxLength = lengthB;
            maxStr = b;
        }else{
            minLength  = lengthB;
            minStr = b;
            maxLength = lengthA;
            maxStr = a;
        }
        String sum="";
        boolean carry = false;
        for(int i=0; i<minLength; i++){
            int digi1 = minStr.charAt(minLength-i-1)-'0';
            int digi2 = maxStr.charAt(maxLength-i-1)-'0';
            int sumDigi;
            if(carry)   sumDigi = digi1+digi2+1;
            else    sumDigi = digi1+digi2;
            if(sumDigi/2>0) carry = true;
            else    carry = false;
            sumDigi = sumDigi%2;
            String curDigi = String.valueOf(sumDigi);
            sum = curDigi +sum;
        }
        for(int i=maxLength-minLength-1; i>=0; i--){
            int digi = maxStr.charAt(i)-'0';
            if(carry) digi = digi+1;
            if(digi==2){
                digi=0;
                carry = true;
            }
            else    carry = false;
            String curDigi = String.valueOf(digi);
            sum = curDigi+sum;
        }
        if(carry)   sum = "1"+sum;
        return  sum;
    }
}