LeetCode_415. Add Strings

415. Add Strings

Easy

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

1. The length of both num1 and num2 is < 5100.
2. Both num1 and num2 contains only digits 0-9.
3. Both num1 and num2 does not contain any leading zero.
4. You must not use any built-in BigInteger library or convert the inputs to integer directly.

package leetcode.easy;

public class AddStrings {

	public String addStrings(String num1, String num2) {

		final int m = num1.length();

		final int n = num2.length();

		int p1 = m - 1, p2 = n - 1;

		int carry = 0;

		StringBuilder sb = new StringBuilder();

		while (p1 >= 0 || p2 >= 0 || carry > 0) {

			int sum = carry + (p1 >= 0 ? num1.charAt(p1) - '0' : 0) + (p2 >= 0 ? num2.charAt(p2) - '0' : 0);

			carry = sum / 10;

			sb.append((char) (sum % 10 + '0'));

			p1--;

			p2--;

		}

		return sb.reverse().toString();

	}

	@org.junit.Test

	public void test() {

		System.out.println(addStrings("0", "0"));

	}

}