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package leetcode;/* Given two binary strings, return their sum (also a binary string). * For example, * a = "11" * b = "1" * Return "100". */import java.lang.Math;public class AddBinary { public String addBinary(String a, String b) { if (a == null || a.length() == 0) //如果a为空,则返回b;反之则返回a return b; if (b == null || b.length() == 0) return a; int i = a.length() - 1; //获取a,b的长 int j = b.length() - 1; int carry = 0; //进位标志,初始化为0 StringBuilder res = new StringBuilder(); while (i >= 0 && j >= 0) { // a,b都不为空时,从后往前遍历,从低位开始相加 int digit = (int) (a.charAt(i) - '0' + b.charAt(j) - '0') + carry; carry = digit / 2; //保存下一个carry位:逢2进位 digit %= 2; //取余,保存当前位(进位后)的值 res.insert(0, digit); //插入到res中 i--; j--; } //a更长时,处理a余下的数位 while (i >= 0) { int digit = (int) (a.charAt(i) - '0') + carry; carry = digit / 2; digit %= 2; res.insert(0, digit); i--; } //b更长时,处理b余下的数位 while (j >= 0) { int digit = (int) (b.charAt(j) - '0') + carry; carry = digit / 2; digit %= 2; res.insert(0, digit); j--; } //加完之后,第一位也需进位 if (carry > 0) { res.insert(0, carry); } return res.toString(); }}
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