Sum of all even numbers in range L and R

Given two integers L and R, the task is to find the sum of all even numbers in range L and R.

Examples:

Input: L = 2, R = 5 
Output: 6
2 + 4 = 6

Input: L = 3, R = 8
Output: 18

Method-1: Iterate from L to R and sum all the even numbers in that range.

Method-2: Find the sum all the natural numbers from L to R and subtract the sum of odd natural numbers in range L to R from it.

Method-3:

  • Find the sum of all even numbers up to R i.e. No. of even numbers up to R will be R/2.
  • Find the sum of all even numbers up to L-1 i.e. No. of even numbers up to L-1 will be (L-1)/2.
  • Then subtract sumUptoL from sumuptoR.

Sum of all even numbers up to any N will be:
R*(R+1) where R = N/2

Below is the implementation of the above approach:

C++

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// C++ program to print the sum
// of all even numbers in range L and R
#include <bits/stdc++.h>
using namespace std;
  
// Function to return the sum of
// all natural numbers
int sumNatural(int n)
{
    int sum = (n * (n + 1));
    return sum;
}
  
// Function to return sum
// of even numbers in range L and R
int sumEven(int l, int r)
{
    return sumNatural(r/2) - sumNatural((l-1) / 2);
}
  
// Driver Code
int main()
{
    int l = 2, r = 5;
    cout << "Sum of Natural numbers from L to R is "
         << sumEven(l, r);
  
    return 0;
}

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Java

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// Java program to print the sum 
// of all even numbers in range L and R 
  
import java.io.*;
  
class GFG {
      
// Function to return the sum of 
// all natural numbers 
static int sumNatural(int n) 
    int sum = (n * (n + 1)); 
    return sum; 
  
// Function to return sum 
// of even numbers in range L and R 
static int sumEven(int l, int r) 
    return sumNatural(r/2) - sumNatural((l-1) / 2); 
  
// Driver Code 
      
    public static void main (String[] args) {
  
        int l = 2, r = 5
        System.out.println ("Sum of Natural numbers from L to R is "+
         sumEven(l, r)); 
    }
}

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Python3

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# Python 3 program to print the sum 
# of all even numbers in range L and R 
  
# Function to return the sum  
# of all natural numbers 
def sumNatural(n):
    sum = (n * (n + 1))
    return int(sum)
  
# Function to return sum 
# of even numbers in range L and R 
def sumEven(l, r):
    return (sumNatural(int(r / 2)) - 
            sumNatural(int((l - 1) / 2)))
  
# Driver Code 
l, r = 2, 5
print("Sum of Natural numbers"
             "from L to R is", sumEven(l, r)) 
  
# This code is contributed 
# by 29AjayKumar

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C#

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// C# program to print the sum 
// of all even numbers in range L and R
  
using System;
  
public class GFG{
          
// Function to return the sum of 
// all natural numbers 
static int sumNatural(int n) 
    int sum = (n * (n + 1)); 
    return sum; 
  
// Function to return sum 
// of even numbers in range L and R 
static int sumEven(int l, int r) 
    return sumNatural(r/2) - sumNatural((l-1) / 2); 
  
// Driver Code 
      
    static public void Main (){
            int l = 2, r = 5; 
        Console.WriteLine("Sum of Natural numbers from L to R is "+
        sumEven(l, r)); 
    }
}

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PHP

Output:

Sum of Natural numbers from L to R is 6


My Personal Notes arrow_drop_up

Just another competitive programmer

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