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 }
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