67. Add Binary

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

The input strings are both non-empty and contains only characters 1 or 0.

Example 1:

Input: a = "11", b = "1"
Output: "100"

Example 2:

Input: a = "1010", b = "1011"
Output: "10101"

翻译：
给你两个二进制字符串，返回他俩的和.

输入字符串都是非空且只包含字符0 1

例 1:

输入: a = "11", b = "1"
输出: "100"

例 2:

输入: a = "1010", b = "1011"
输出: "10101"

C程序
学习的代码

char * addBinary(char * a, char * b){
    int alen = strlen(a);
    int blen = strlen(b);
    int Mlen = alen>blen?alen:blen;   
    int carry = 0;
    
    char * result = (char*)malloc(Mlen+2);
    result[Mlen+1]='\0';
   
    while(alen!=0 || blen!=0)
    {
    	//减去‘0’是为了将字符转化为整形
        if(alen)carry += a[--alen]-'0';
        if(blen)carry += b[--blen]-'0';
        result[Mlen--] = (int)(carry%2) + '0';     
        carry = (int)(carry/2);
    } 
 	//如果不加这字符串的结束标志，就会出现堆溢出
	result[0] = carry+'0';
    //能直接把数组开头截掉，很好的技巧
    return result+(carry^1);
}

总结：

1. 可以通过增加数组头地址，能够返回一个被截掉头的数组
2. 对于字符串数组，如果后面没有加字符串结束标志‘\0’，那么在进行字符串读取时会发生堆溢出