Find the Sum of Numbers in a given Range in Python
Find the Sum of the Numbers in a Given Range
Given two integer inputs as the range [ low , high ], the objective is to find the sum of the numbers that lay in the intervals given by the integer inputs. Therefore we’ll write a code to Find the Sum of the Numbers in a Given Range in Python Language.
Example Input : 2 5 Output : 14
Find the Sum of the Numbers in a Given Interval in Python Language
Given two integer inputs as the range [low , high], the objective is to find the sum of all the numbers that lay in the given integer inputs as interval. In order to do so we usually iterate through the the numbers in the given range and keep appending them to the sum variable. Here are few methods to solve the above mentioned problem in Python Language.
- Method 1: Using Brute Force
- Method 2: Using the Formula
- Method 3: Using Recursion
We’ll discuss the above mentioned methods in detail in the sections below.
Method 1: Using Brute Force
In this method we’ll use loops like for, while and do while to sum all the numbers that lay in the intervals of the given input integers.
Working
For in integer inputs num1 and num2 as the intervals
- Initialize the required variables.
- Run a for loop from num1 to num2+1 i.e [num1,num2].
- Append i to sum variable with each iteration.
- Print sum variable.
Let’s implement the above logic in Python Language.
Python Code
num1, num2 = 3, 6 sum = 0 for i in range(num1,num2+1): sum+=i print(sum)
Output
18
Method 2: Using the Formula
In this method we’ll use formula mentioned below to find the sum of all the numbers that lay in the interval given by the input variable.
The formula to find the sum of n natural numbers is:
Sum = n * ( n + 1 ) / 2
Therefore in order to find the sum in a given interval we'll minus the sum of the numbers until the lower range from the whole sum and add an offset as the lowest bound is itself included in the summation. Hence the final formula is :
Sum = b * ( b + 1 ) / 2 – a * ( a + 1 ) / 2 + a .
Working
For the two integer inputs num1 and num2
- Initialize the required variables.
- perform sum = int((num2*(num2+1)/2) – (num1*(num1+1)/2) + num1).
- Print Sum variable.
Let’s implement the above logic in Python Language.
Python Code
num1, num2 = 3, 6 sum = int((num2*(num2+1)/2) - (num1*(num1+1)/2) + num1) print(sum)
Output
18
Method 3: Using Recursion
In this method we’ll use recursion to find the sum of all the numbers that lay in the interval given by the input variable. To know more about recursion, refer to Recursion in Python.
Working
For the two integer inputs num1 and num2 as the interval
- Initialize the required variables.
- Define a recursive function with base case as num1>num2.
- Set the recursive step call as num1 + recursum(sum, num1+1, num2).
- call the recursum() function and print the returned value.
Let’s implement the above logic in Python Language.
Python Code
def recursum(sum,num1,num2):
if num1 > num2:
return sum
return num1 + recursum(sum,num1+1,num2)
num1, num2 = 3, 6
sum = 0
print(recursum(sum,num1,num2))
Output
18
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N1 = int(input(“Enter the first number : “))
N2 = int(input(“Enter the second number : “))
sum = 0
for i in range(N1,N2+1):
sum += i
print(f”sum is {sum}”)