[leetcode]415. Add Strings字符串相加

public String addStrings(String num1, String num2) {
        StringBuilder res = new StringBuilder();
        StringBuilder s1 = new StringBuilder(num1);
        StringBuilder s2 = new StringBuilder(num2);
        int flag = 0;
        while (s1.length()>0||s2.length()>0||flag!=0)
        {
            int cur = 0;
            if (s1.length()>0) {
                cur+=s1.charAt(s1.length()-1)-'0';
                s1.deleteCharAt(s1.length()-1);
            }
            if (s2.length()>0) {
                cur+=s2.charAt(s2.length()-1)-'0';
                s2.deleteCharAt(s2.length()-1);
            }
            cur+=flag;
            if (cur>9) flag = 1;
            else flag = 0;
            res.append(cur%10);
        }
        return res.reverse().toString();
    }

直接对字符串进行操作