咨詢區

• Matthew Watson：

我記得 .net core 中有一個版本對下面的場景做了一個優化，代碼如下：

int?smallest?=?new[]{?7,?2,?4,?6,?0,?1,?6,?9,?8?}.OrderBy(i?=>?i).First();

在很早之前它的時間復雜度是 O(N.Log(N))，現在已經優化成 O(N) 了。

為了驗證，我用 .NET Core 和 .NET Framework 來跑下面的這段代碼，參考如下：

using?System; using?System.Collections.Generic; using?System.Linq;namespace?Demo {static?class?Program{static?void?Main(){int[]?test?=?{?7,?2,?4,?6,?0,?1,?6,?9,?8?};var?comparer?=?new?Comparer();var?_?=?test.OrderBy(i?=>?i,?comparer).First();}}class?Comparer?:?IComparer<int>{public?int?Compare(int?x,?int?y){Console.WriteLine($"Comparing?{x}?with?{y}");return?x.CompareTo(y);}} }

如果你想試試的話，可以參考如下兩個在線工具。

.NET Framework: https://dotnetfiddle.net/XItXYL

.NET Core: https://dotnetfiddle.net/swlc0O

.NET Framework 4.8

Comparing?0?with?7 Comparing?0?with?8 Comparing?0?with?9 Comparing?0?with?6 Comparing?0?with?1 Comparing?0?with?0 Comparing?0?with?2 Comparing?0?with?6 Comparing?0?with?4 Comparing?0?with?2 Comparing?0?with?0 Comparing?7?with?2 Comparing?7?with?4 Comparing?7?with?6 Comparing?7?with?7 Comparing?7?with?8 Comparing?7?with?9 Comparing?7?with?6 Comparing?7?with?1 Comparing?7?with?7 Comparing?7?with?1 Comparing?9?with?7 Comparing?9?with?9 Comparing?9?with?8 Comparing?7?with?7 Comparing?7?with?8 Comparing?7?with?7 Comparing?6?with?2 Comparing?6?with?4 Comparing?6?with?6 Comparing?6?with?1 Comparing?6?with?6 Comparing?6?with?6 Comparing?6?with?1 Comparing?6?with?6 Comparing?6?with?6 Comparing?4?with?2 Comparing?4?with?4 Comparing?4?with?1 Comparing?2?with?2 Comparing?2?with?1

.NET Core 3.1

Comparing?2?with?7 Comparing?4?with?2 Comparing?6?with?2 Comparing?0?with?2 Comparing?1?with?0 Comparing?6?with?0 Comparing?9?with?0 Comparing?8?with?0

最后提一下，大家記得在哪里看到這樣的文檔記載嗎？不是官方的就不要發了。

回答區

• Matthew Watson：

確實，對這個進行優化的文檔說明是有的，可以參考下 Github: ?https://github.com/dotnet/runtime/issues/14867 上的這個討論和最后的編碼實現。

點評區

由 O(N.Log(N)) 變成 O(LogN),這確實是一個非常大的性能提升，我們的基礎庫真的是越來越強大 🐂👃。

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