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.

 public class Solution {
     public String addBinary(String a, String b) {
         if (a == null || b == null) {
             return null;
         }

         if (a.length() == 0) {
             return b;
         }

         if (b.length() == 0) {
             return a;
         }

         StringBuilder sb = new StringBuilder();

         int p1 = a.length() - 1;
         int p2 = b.length() - 1;

         int carry = 0;
         while (p1 >= 0 || p2 >= 0) {
             int sum = carry;
             if (p1 >= 0) {
                 sum += (a.charAt(p1) - '0');
             }

             if (p2 >= 0) {
                 sum += (b.charAt(p2) - '0');
             }

             char c = sum % 2 == 1 ? '1': '0';
             sb.insert(0, c);
             carry = sum / 2;

             p1--;
             p2--;
         }

         if (carry == 1) {
             sb.insert(0, '1');
         }

         return sb.toString();
     }
 }

GITHUB CODE:

AddBinary.java