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Add Binary

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

For example,

Java代码：

public class Solution {    public String addBinary(String a, String b) {        int len = a.length();		if (len > b.length())			len = b.length();		StringBuilder sb = new StringBuilder("");		int flag = 0;		for (int i = 0; i < len; i++) {			if (a.charAt(a.length() - 1 - i) != b.charAt(b.length() - 1 - i)) {				if (flag == 1) {					flag = 1;					sb.append("0");				} else					sb.append("1");			} else {				if (flag == 1) {					sb.append("1");					flag = 0;				} else					sb.append("0");				if (a.charAt(a.length() - 1 - i) == '1') {					flag = 1;				}			}		}		if (len == a.length()) {			for (int i = len; i < b.length(); i++) {				if (b.charAt(b.length() - 1 - i) == '0') {					if (flag == 1) {						flag = 0;						sb.append("1");					} else {						sb.append("0");					}				} else {					if (flag == 1) {						sb.append("0");					} else {						sb.append("1");					}				}			}		} else {			for (int i = len; i < a.length(); i++) {				if (a.charAt(a.length() - 1 - i) == '0') {					if (flag == 1) {						flag = 0;						sb.append("1");					} else {						sb.append("0");					}				} else {					if (flag == 1) {						sb.append("0");					} else {						sb.append("1");					}				}			}		}		if (flag == 1) {			flag = 0;			sb.append("1");		}		sb.reverse();		return sb.toString();    }}

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