Leetcode: Add Strings
Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2. Note: The length of both num1 and num2 is < 5100. Both num1 and num2 contains only digits 0-9. Both num1 and num2 does not contain any leading zero. You must not use any built-in BigInteger library or convert the inputs to integer directly.
1 public class Solution { 2 public String addStrings(String num1, String num2) { 3 StringBuffer res = new StringBuffer(); 4 int i = num1.length()-1; 5 int j = num2.length()-1; 6 int carry = 0; 7 while (i>=0 || j>=0 || carry!=0) { 8 int sum = 0; 9 if (i >= 0) { 10 sum += (int)(num1.charAt(i) - '0'); 11 i--; 12 } 13 if (j >= 0) { 14 sum += (int)(num2.charAt(j) - '0'); 15 j--; 16 } 17 if (carry != 0) { 18 sum += carry; 19 } 20 int digit = sum % 10; 21 carry = sum / 10; 22 res.insert(0, digit); 23 } 24 return res.toString(); 25 } 26 }