[LeetCode]Add Binary

题目描述

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

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

解题思路

将两个字符串从后向前扫描，相同位的字符变为数字后进行相加运算，需要考虑到进位和两字符串不等长的情况。

代码

	public static String addBinary(String a, String b) {
		String result = "";

		if (a == null && b == null) {
			return null;
		} else {
			if (a == null)
				return b;
			if (b == null)
				return a;
		}
        
		int x = 0, y = 0, add = 0;
		
		for(int i = a.length() - 1,j = b.length() - 1; i >= 0 || j >=0;i--,j--){
			x = 0;
			if (i >= 0) {
				x = a.charAt(i) - '0';
			}
			
			y = 0;
			if (j >= 0) {
				y = b.charAt(j) - '0';
			}
			result = (x + y + add) % 2 + result;
			add = (x + y + add) / 2;
		}
		
		if (add == 1) {
			result = 1 + result;
		}
		return result;
	}