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Add Binary 

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

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

分析

  题目的意思是，给定两个只包含字符‘0’和‘1’的字符串，返回表示它们的二进制和的字符串。


     * 一道很简单的程序设计题目。

Code

class Solution {
public:
    /* 
     * 简单的程序设计题目
     *
     * */
    string addBinary(string a, string b) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        int len_a = a.size();
        int len_b = b.size();
        if(!len_a)  return b;
        if(!len_b)  return a;
        //返回的和字符串长度应该不超过a和b最大长度+1
        int len_sumStr = std::max(len_a, len_b) + 1;
        string sumStr(len_sumStr, '0');
        int pSum = len_sumStr-1, pA = len_a -1, pB = len_b - 1;
        int carry = 0;
        int lhs, rhs, tempSum;
        while(len_a >= 0 || len_b >= 0)
        {
            if(len_a >= 0)
                lhs = a[len_a] - '0';
            else
                lhs = 0;
            if(len_b >= 0)
                rhs = b[len_b] - '0';
            else
                rhs = 0;
            tempSum = lhs + rhs + carry;
            if(tempSum > 1)
                carry = 1, tempSum -= 2;
            else
                carry = 0;
            sumStr[len_sumStr] = tempSum + '0';
            len_a--, len_b--, len_sumStr--;         
        }
        if(carry)
        {
            sumStr[0] = '1';
            return sumStr;
        } 
        //如果首位为0，需要去掉第一位，以非0开头
        else
           return sumStr.substr(1, len_sumStr-1); 
    }
};

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