C#版 - 剑指Offer 面试题35：第一个只出现一次的字符 解题报告

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using System.Collections.Generic;
using System.Linq;

namespace AimedAtOffer35
{
    public class Program
    {
        public static char FirstNotRepeatingChar(string str)
        {
            char res = new char();
            Dictionary<char, int> dict = new Dictionary<char, int>();
            if (str.Length == 0)
                return '\0';

            for (int i = 0; i < str.Length; i++)
            {
                if (!dict.ContainsKey(str[i]))
                    dict.Add(str[i], 1);
                else
                    dict[str[i]]++;
            }
            res = dict.FirstOrDefault(p => p.Value == 1).Key; //LINQ是C#3.0中引入的，可以直接用，目前C#已到7.0版

            return res;
        }

        public static void Main()
        {
            string line;
            while ((line = System.Console.ReadLine()) != null)
            {
                string str= line;
                var ch = FirstNotRepeatingChar(str);
                if (ch == '\0')
                {
                    System.Console.WriteLine(-1);
                }
                else System.Console.WriteLine(ch);
            }
        }
    }
}

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    var res = (FirstNotRepeatingChar(str) == '\0') ? -1 : FirstNotRepeatingChar(str);
    // var即使改为dynamic，在WriteLine时均会输出其ASCII码数字
    System.Console.WriteLine(res);