LeetCode: Add Binary 解题报告

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

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

 

SOLUTION:

指针指到两个字符串的末尾，不断往前推进，用carry表示进位。用stringbuilder来记录结果。

使用insert(0, c)函数将加出的结果不断插入到STRINGBUILDER.

 1 public class Solution {

 2     public String addBinary(String a, String b) {

 3         if (a == null || b == null) {

 4             return null;

 5         }

 6         

 7         if (a.length() == 0) {

 8             return b;

 9         }

10         

11         if (b.length() == 0) {

12             return a;

13         }

14         

15         StringBuilder sb = new StringBuilder();

16         

17         int p1 = a.length() - 1;

18         int p2 = b.length() - 1;

19         

20         int carry = 0;

21         while (p1 >= 0 || p2 >= 0) {

22             int sum = carry;

23             if (p1 >= 0) {

24                 sum += (a.charAt(p1) - '0');

25             }

26             

27             if (p2 >= 0) {

28                 sum += (b.charAt(p2) - '0');

29             }

30             

31             char c = sum % 2 == 1 ? '1': '0';

32             sb.insert(0, c);

33             carry = sum / 2;

34             

35             p1--;

36             p2--;

37         }

38         

39         if (carry == 1) {

40             sb.insert(0, '1');    

41         }

42         

43         return sb.toString();

44     }

45 }

View Code

 

GITHUB CODE:

AddBinary.java