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 }

GITHUB CODE:

AddBinary.java