Add Strings
Description
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.
Hint
Train of Thought
Code
public class Solution { public String addStrings(String num1, String num2) { StringBuilder sb = new StringBuilder(); int carry = 0; for(int i = num1.length() - 1, j = num2.length() - 1; i >= 0 || j >= 0; i--, j--){ int x = i < 0 ? 0 : num1.charAt(i) - '0'; int y = j < 0 ? 0 : num2.charAt(j) - '0'; sb.append((x + y + carry) % 10); carry = (x + y + carry) / 10; } if(carry != 0) sb.append(carry); return sb.reverse().toString(); } }