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"));
	}
}