判斷字符串中是否存在的幾種方案：string.indexof、string.contains、list.contains、list.any幾種方式效率對比

我們在做項目時，可能會遇到這樣的需求，比如判斷,1,2,3,33,22,123, 中是否存在,3,。

var str=",1,2,3,33,22,123,";

一般有幾種方式：

1、str.IndexOf(",3,")>=0

2、str.Contains(",3,")

有可能我們不用字符串而用List來存，判斷list中是否存在3

var list = str.Split(',').ToList();

3、list.Contains("3");

4、List.Any(t=>t=="3");

接下來就驗證一下上面4種方案究竟哪種效率最高？

public void Test()
        {
            var str = "article.add,article.update,article.delete,article.view," +
                "category.add,category.update,category.delete,category.view," +
                "user.add,user.update,user.delete,user.view," +
                "role.add,role.update,role.delete,role.view," +
                "news.add,news.update,news.delete,news.view," +
                "category.add,category.update,category.delete,category.view," +
                "Threading.add,Threading.update,Threading.delete,Threading.view," +
                "System.add,System.update,System.delete,System.view," +
                "Generic.add,Generic.update,Generic.delete,Generic.view," +
                "Collections.add,Collections.update,Collections.delete,Collections.view," +
                "Tasks.add,Tasks.update,Tasks.delete,Tasks.view," +
                "CslApp.add,CslApp.update,CslApp.delete,CslApp.view";
            var list = str.Split(',').ToList();

            var str1 = "Tasks2.view"; //這里查詢一個不存在的字符串，這樣更費時，如果字符串存在，話費的時間要少些。
            var count = 100000;
            Stopwatch sw = new Stopwatch();
            sw.Start();
            //耗時巨大的代碼
            for (int i = 0; i < count; i++)
            {
                if (str.Contains(str1)) { }
            }
            sw.Stop();
            TimeSpan ts = sw.Elapsed;
            Console.WriteLine("string.contains總共花費{0}ms.", ts.TotalMilliseconds);

            Stopwatch sw2 = new Stopwatch();
            sw2.Start();
            //耗時巨大的代碼 
            for (int i = 0; i < count; i++)
            {
                if (list.Contains(str1)) { }
            }
            sw2.Stop();
            TimeSpan ts2 = sw2.Elapsed;
            Console.WriteLine("List.Contains總共花費{0}ms.", ts2.TotalMilliseconds);

            Stopwatch sw3 = new Stopwatch();
            sw3.Start();
            //耗時巨大的代碼 
            for (int i = 0; i < count; i++)
            {
                if (list.Any(t=>t == str1)) { }
            }
            sw3.Stop();
            TimeSpan ts3 = sw3.Elapsed;
            Console.WriteLine("List.Any總共花費{0}ms.", ts3.TotalMilliseconds);

            Stopwatch sw4 = new Stopwatch();
            sw4.Start();
            //耗時巨大的代碼 
            for (int i = 0; i < count; i++)
            {
                if (str.IndexOf(str1)>=0) { }
            }
            sw4.Stop();
            TimeSpan ts4 = sw4.Elapsed;
            Console.WriteLine("string.IndexOf總共花費{0}ms.", ts4.TotalMilliseconds);

        }

　　這里分別循環十萬次來測試，得到的結果：

可以看出，IndexOf >=0這種方式簡直是災難性的存在，

效率最高的是將字符串轉成List在用List.Contains判斷，

List.Any查詢效率都遠不如string.Contains和List.Contains。

下面運行100萬次的結果，由於indexof效率實在太差太費時間，就去掉了這個判斷，

可見，轉換成List在用list.Contains判斷效率是最高的。