Given two non-negative integers num1
and num2
represented as string, return the sum of num1
and num2
.
Note:
- The length of both
num1
andnum2
is < 5100. - Both
num1
andnum2
contains only digits0-9
. - Both
num1
andnum2
does not contain any leading zero. - You must not use any built-in BigInteger library or convert the inputs to integer directly.
time: O(n), space: O(1)
class Solution { public String addStrings(String num1, String num2) { StringBuilder sb = new StringBuilder(); int i = num1.length() - 1, j = num2.length() - 1, carry = 0; while(i >= 0 || j >= 0) { int sum = carry; if(i >= 0) sum += num1.charAt(i) - '0'; if(j >= 0) sum += num2.charAt(j) - '0'; sb.append(sum % 10); carry = sum / 10; i--; j--; } if(carry != 0) { sb.append(carry); } return sb.reverse().toString(); }}