Add Binary

[size=large][color=darkred][b]题目描述[/b][/color][/size]
Given two binary strings, return their sum (also a binary string).

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

[size=large][color=darkred][b]解题思路[/b][/color][/size]
本题考查对字符串和容器的使用。主要思想是将a,b转化为列表处理，然后从低位到高位一次进行进位操作。

[size=large][color=darkred][b]相关知识点[/b][/color][/size]
[size=medium][b]（1）对一个容器进行逆序操作[/b][/size]

Collections.reverse(list);

[size=large][color=darkred][b]自己的代码[/b][/color][/size]

package leetcode;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class AddBinary {
	public String addBinary(String a, String b) {
		if(a == null || b == null) return null;
		if(a.length() == 0) return b;
		if(b.length() == 0) return a;

		//较短为b,较长的为a
		if(a.length() < b.length()) {
			String temp = a;
			a = b;
			b = temp;
		}

		List<Integer> aList = new ArrayList<Integer>();
		for(int i = a.length() - 1; i >= 0; i--) aList.add((a.charAt(i)=='0') ? 0 : 1);
		List<Integer> bList = new ArrayList<Integer>();
		for(int i = b.length() - 1; i >= 0; i--) bList.add((b.charAt(i)=='0') ? 0 : 1);
		for(int i = 0; i < a.length()-b.length(); i++) bList.add(0);

		int carry = 0;
		for(int i = 0; i < aList.size(); i++){
			int result = aList.get(i) + bList.get(i) + carry;
			if(result > 1){
				carry = 1;
				if(result == 2) aList.set(i, 0);
				if(result == 3) aList.set(i, 1);
			}
			else{
				carry = 0;
				aList.set(i, result);
			}
		}
		if(carry != 0) aList.add(1);
		Collections.reverse(aList);
		String s = "";
		for(int i : aList) s += i;

        return s;
    }

	public static void main(String[] args) {
		String a = "11";
		String b = "1";

		AddBinary ab = new AddBinary();
		System.out.println(ab.addBinary(a, b));
	}
}