如何使查找数组中第N个最频繁元素的过程更高效，更紧凑？ [英] How can I make my procedure for finding the Nth most frequent element in an array more efficient and compact?

问题描述

这是我想出的解决方案的一个例子

Here's an example of a solution I came up with

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

public class Program
{
    public static void Main()
    {
        int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 }; 
        var countlist = arr.Aggregate(new Dictionary<int,int>(), (D,i) => { 
                                        D[i] = D.ContainsKey(i) ? (D[i] + 1) : 1;
                                        return D; 
                                      })
                            .AsQueryable()
                            .OrderByDescending(x => x.Value)
                            .Select(x => x.Key)
                            .ToList();
        // print the element which appears with the second 
        // highest frequency in arr
        Console.WriteLine(countlist[2]); // should print 3
    }
}

至少想找出如何

• 将查询子句至少减少一个。虽然我看不到任何冗余，但这是LINQ查询的类型，在这里我担心创建的所有中间结构的所有开销。

• Cut down the query clauses by at least one. While I don't see any redundancy, this is the type of LINQ query where I fret about all the overhead of all the intermediate structures created.

弄清楚如何不在末尾返回整个列表。我只想列举序列中的第二个元素；我不需要出于从列表中删除单个元素的目的而返回整个列表。

Figure out how to not return an entire list at the end. I just want the 2nd element in the enumerated sequence; I shouldn't need to return the entire list for the purpose of getting a single element out of it.

推荐答案

int[] arr = new int[] { 1, 2, 2, 3, 3, 3, 4, 4, 4, 4 };

var lookup = arr.ToLookup(t => t);
var result = lookup.OrderByDescending(t => t.Count());

Console.WriteLine(result.ElementAt(1).Key);

这篇关于如何使查找数组中第N个最频繁元素的过程更高效，更紧凑？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！