Add Binary

把短的串添加0变为一样长度的字符串。

public class Solution {
	public String addBinary(String a, String b) {
		// Start typing your Java solution below
		// DO NOT write main() function

		int len_a = a.length();
		int len_b = b.length();
		if (len_a == 0 && len_b == 0)
			return null;
		if (len_a == 0)
			return b;
		if (len_b == 0)
			return a;
		int max;
		StringBuilder sb = new StringBuilder();
		StringBuilder ret = new StringBuilder();

		if (len_a < len_b) {
			for (int i = 0; i < len_b - len_a; i++)
				sb.append(0);
			sb.append(a);
			max = len_b;
			a = sb.toString();
		} else if (len_a > len_b) {
			for (int i = 0; i < len_a - len_b; i++)
				sb.append(0);
			sb.append(b);
			max = len_a;
			b = sb.toString();
		} else {
			max = len_a;
		}

		int[] c = new int[max];
		int t = 0;
		int i;
		for (i = 0; i < max; i++) {
			char ca = a.charAt(max - i - 1);

			char cb = b.charAt(max - i - 1);
			if (ca == '1' && cb == '1') {
				c[i] = t;
				t = 1;
			}
			if ((ca == '1' && cb == '0') || (ca == '0' && cb == '1')) {
				c[i] = (t + 1) % 2;
				if (t == 0)
					t = 0;
				else
					t = 1;
			}
			if (ca == '0' && cb == '0') {
				c[i] = t;
				t = 0;
			}
		}
		if (t == 1) {
			ret.append(1);
		}
		for (i = max - 1; i >= 0; i--)
			ret.append(c[i]);
		return ret.toString();
	}

	public static void main(String[] args) {
		Solution aa = new Solution();
		System.out.println(aa.addBinary("11", "1"));
	}
}