How to Calculate the Summation of a Number in Java

The challenge

Write a program that finds the summation of every number from 1 to num. The number will always be a positive integer greater than 0.

For example:

summation(2) -> 3
1 + 2

summation(8) -> 36
1 + 2 + 3 + 4 + 5 + 6 + 7 + 8

The solution in Java

public class Solution {

    public static int summation(int n) {
        int runningTotal = 0;
      
        for (int i=1; i<=n; i++) runningTotal += i;
      
        return runningTotal;
    }
}

A simpler alternative is to do the following:

public class Solution {

    public static int summation(int n) {

        return  n*(n+1)/2;
    }
}

This can also be solved using recursion:

public class Solution {

    public static int summation(int n) {
        if (n == 1)
          return 1;
        return summation(n-1) + n;
    }
}

Test cases to validate our code

import java.util.Random;
import static org.junit.Assert.assertEquals;
import org.junit.Test;

public class SolutionTest {
    @Test
    public void test1() {
        assertEquals(1,
        Solution.summation(1));
    }
    @Test
    public void test2() {
        assertEquals(36,
        Solution.summation(8));
    }
}
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