why getting the sum of numbers is not equal if I use Enumerable.Range?-CodePudding

Recently I was playing on CodingGame, normally I use "for" the challenges, but this time I've been using "Enumerable.Range" and something weird happened.

If N = 1001, the value of "result1" should be 250500, but the output was 251502, why?

But when N = 1000, the values of result1 and result2 are equals, why?


using System;
using System.Linq;
using System.IO;
using System.Text;
using System.Collections;
using System.Collections.Generic;

class Solution
{
    static void Main(string[] args)
    {
        int N = int.Parse("1001");

        var list = Enumerable.Range(2, N);
        long result1 = list.Sum(item =>
        {
            return item % 2 == 0 ? item : 0;
        });
        
        long result2 = 0;
        for (int i = 2; i <= N; i  )
        {
            if (i % 2 == 0) result2  = i;
        }

        Console.WriteLine(result1);
        Console.WriteLine(result2);
    }
}

CodePudding user response：

Enumerable.Range like this

   Enumerable.Range(2, 1001)

Generates 1001 numbers starting with 2. The second argument is the count of numbers to generate, not the end value. https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.range?view=net-6.0

CodePudding user response：

It's just because the second argument of the Enumerable.Range method is the count of elements but not the upper bound. Therefore the returning sequence is 2 .. 1002.