LeetCode61|字符串相加

 
public class AddStringsTest {
    public static void main(String[] args) {
        String s1 = "123";
        String s2 = "456";
        String s = addStrings(s1, s2);
        System.out.println("s = " + s);

    }

    public static String addStrings(String num1, String num2) {
        if (num1 == null || num1.length() == 0) {
            return num2;
        }
        if (num2 == null || num2.length() == 0) {
            return num1;
        }
        StringBuilder stringBuilder = new StringBuilder();
        int num1Length = num1.length() - 1;
        int num2Length = num2.length() - 1;
        int carry = 0;
        while (num1Length >= 0 || num2Length >= 0 || carry > 0) {
            if (num1Length >= 0) {
                carry += (num1.charAt(num1Length) - '0');
                num1Length -= 1;
            }
            if (num2Length >= 0) {
                carry += (num2.charAt(num2Length) - '0');
                num2Length -= 1;
            }
            stringBuilder.append(carry % 10);
            carry /= 10;
        }
        return stringBuilder.reverse().toString();
    }
}