415. 字符串相加

415. 字符串相加 - 力扣（LeetCode）

class Solution {
    public String addStrings(String num1, String num2) {
  
        StringBuffer result = new StringBuffer();
        int i = num1.length() - 1;
        int j = num2.length() - 1;
        int tmp = 0;
        int carry = 0;

        while(i>=0 || j>=0 || carry!=0){
            int n1 = i >=0 ? num1.charAt(i) - '0' : 0;
            int n2 = j >=0 ? num2.charAt(j) - '0' : 0;
            tmp = n1 + n2 + carry;
            result.append(tmp%10);            
            carry = tmp/10;
            i--;
            j--;
        }

        return result.reverse().toString();

    }
}