Sum of Series

Sum of Series

Problem Statement

Write a program to find the sum of the given series 1+2+3+ . . . . . .(N terms).

Example 1

Input :
N = 1

Output : 1

Explanation :
For n = 1, sum will be 1.

Example 2

Input :
N = 5

Output : 15

Explanation :
For n = 5, sum will be 1 + 2 + 3 + 4 + 5 = 15.

Task

Complete the function seriesSum() which takes single integer n, as input parameters and returns an integer denoting the answer. You don't need to print the answer or take inputs.

Expected Time Complexity : O(1)
Expected Auxiliary Space : O(1)

Constraints :
1 <= N <= 10⁵

Solutions

Java Solution

class Solution {
    // function to return sum of  1, 2, ... n
    long seriesSum(int n) {
        // code here
        long m = n;
        long sum = (m*(m+1)/2);
        return sum;
    }
}
        
    

C++ Solution

class Solution {
public:
 // function to return sum of  1, 2, ... n
 long long seriesSum(int n) {
     // code here
     long long sum = n;
     return sum*(sum+1)/2;
 	}
};