Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 as a string.
Example 1:
Input: num1 = "11", num2 = "123"
Output: "134"
Example 2:
Input: num1 = "456", num2 = "77"
Output: "533"
Example 3:
Input: num1 = "0", num2 = "0"
Output: "0"
Constraints:
- 1 <= num1.length, num2.length <= 104
- num1 and num2 consist of only digits.
- num1 and num2 don't have any leading zeros except for the zero itself.
Follow up: Could you solve it without using any built-in BigInteger library or converting the inputs to integer directly?
class Solution {
public String addStrings(String num1, String num2) {
int i = num1.length()-1;
int j = num2.length()-1;
int carry = 0;
String res = "";
while(i>=0||j>=0){
if(i>=0){
carry += num1.charAt(i--)-'0';
}
if(j>=0){
carry += num2.charAt(j--)-'0';
}
res = Integer.toString(carry%10) + res;
carry/=10;
}
return carry==0?res:"1"+res;
}
}class Solution {
public String addStrings(String num1, String num2) {
int i = num1.length()-1;
int j = num2.length()-1;
int carry = 0;
StringBuilder sb = new StringBuilder();
while(i>=0||j>=0){
if(i>=0){
carry += num1.charAt(i--)-'0';
}
if(j>=0){
carry += num2.charAt(j--)-'0';
}
sb.append(carry%10);
carry /= 10;
}
sb = carry==0?sb:sb.append("1");
return sb.reverse().toString();
}
}