leetcode415

public class Solution
    {
        public string AddStrings(string num1, string num2)
        {
            //判断num1和num2的长度，进行对齐
            if (num1.Length < num2.Length)
            {
                //将num1前补0
                var zerocount = num2.Length - num1.Length;
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < zerocount; i++)
                {
                    sb.Append("0");
                }
                num1 = sb.ToString() + num1;
            }
            else
            {
                var zerocount = num1.Length - num2.Length;
                StringBuilder sb = new StringBuilder();
                for (int i = 0; i < zerocount; i++)
                {
                    sb.Append("0");
                }
                num2 = sb.ToString() + num2;
            }

            //对齐之后，从低位到高位依次进行加运算

            var step = 0;//进位

            var list1 = num1.Reverse().ToList();
            var list2 = num2.Reverse().ToList();
            StringBuilder sb2 = new StringBuilder();
            for (int i = 0; i < list1.Count(); i++)
            {
                var n1 = Convert.ToInt32(list1[i].ToString());
                var n2 = Convert.ToInt32(list2[i].ToString());

                var n = n1 + n2 + step;
                sb2.Append((n % 10).ToString());
                if (n >= 10)
                {
                    step = 1;
                }
                else
                {
                    step = 0;
                }
            }

            if (step == 1)
            {
                sb2.Append("1");
            }

            var list = sb2.ToString().Reverse();

            StringBuilder sb3 = new StringBuilder();
            foreach (var c in list)
            {
                sb3.Append(c);
            }

            var result = sb3.ToString();
            return result;
        }
    }

https://leetcode.com/problems/add-strings/#/description