Add Binary @LeetCode

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

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

	package leetcode;
	/**
	*
	* Solution: Same to Add Two Number but there's a lot of useful tips not very easy to handle.
	* 1. Need to identify which string is shorter.(Make sure a is longer, if not, swap) --> only judge once aIndex >= 0
	* 2. Concatenate result using string make is easier and don't need to consider boundary and shift.
	*
	* Similiar Question: Add Two number
	* @author jeffwan
	* @date Apr 1, 2014
	*/
	public class AddBinary {
	public String addBinary(String a, String b) {
	if (a.length() < b.length()) {
	String temp = a;
	a = b;
	b = temp;
	}
	int aIndex = a.length() - 1;
	int bIndex = b.length() - 1;
	int carry = 0;
	String result = "";
	while(bIndex >= 0) {
	int sum = carry + Character.getNumericValue(a.charAt(aIndex))
	+ Character.getNumericValue(b.charAt(bIndex));
	result = String.valueOf(sum % 2) + result;
	carry = sum / 2;
	aIndex--;
	bIndex--;
	}
	while(aIndex >=0) {
	int sum = carry + Character.getNumericValue(a.charAt(aIndex));
	result = String.valueOf(sum % 2) + result;
	carry = sum / 2;
	aIndex--;
	}
	if (carry != 0) {
	result = String.valueOf(carry) + result;
	}
	return result;
	}
	/**
	* My solution transfer String to Int is dangerous, it faces many problems like Integer Boundary.
	* Easiest way is to operate char or string directly.
	* Failed Test case: "1110110101", "1110111011" Output: "2147483647" Expected:"11101110000"
	*/
	public String addBinary2(String a, String b) {
	int carry = 0;
	int result = 0;
	int i = a.length() - 1, j = b.length() - 1;
	int flag = 0;
	for (; i >= 0 && j >= 0; i--, j--) {
	int aNum = Character.getNumericValue(a.charAt(i));
	int bNum = Character.getNumericValue(b.charAt(j));
	int sum = aNum + bNum + carry;
	result += sum % 2 * Math.pow(10, flag);
	carry = sum / 2;
	flag++;
	}
	while (i >= 0) {
	int sum = carry + Character.getNumericValue(a.charAt(i));
	result += sum % 2 * Math.pow(10, flag);
	carry = sum / 2;
	flag++;
	i--;
	}
	while (j >= 0) {
	int sum = carry + Character.getNumericValue(b.charAt(j));
	result += sum % 2 * Math.pow(10, flag);
	carry = sum / 2;
	flag++;
	j--;
	}
	if (carry != 0) {
	result += Math.pow(10, flag);
	}
	return String.valueOf(result);
	}
	}

view raw AddBinary.java hosted with ❤ by GitHub