Description
Given two non-negative integers 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.
Solution
class Solution {
public String addStrings(String num1, String num2) {
StringBuilder sum = new StringBuilder();
int carry = 0;
int len1 = num1.length();
int len2 = num2.length();
for (int i = 0; i < Math.max(len1, len2); ++i) {
if (i < len1) {
carry += num1.charAt(len1 - 1 - i) - '0';
}
if (i < len2) {
carry += num2.charAt(len2 - 1 - i) - '0';
}
sum.insert(0, carry % 10);
carry /= 10;
}
if (carry > 0) {
sum.insert(0, carry);
}
return sum.toString();
}
}
