[자바스크립트로 구현한 알고리즘] Beginner Series #3 Sum of Numbers

Given two integers, which can be positive and negative, find the sum of all the numbers between including them too and return it. If both numbers are equal return a or b. Note! a and b are not ordered! 

Example: 

GetSum(1, 0) == 1 // 1 + 0 = 1 

GetSum(1, 2) == 3 // 1 + 2 = 3 

GetSum(0, 1) == 1 // 0 + 1 = 1 

GetSum(1, 1) == 1 // 1 Since both are same 

GetSum(-1, 0) == -1 // -1 + 0 = -1 

GetSum(-1, 2) == 2 // -1 + 0 + 1 + 2 = 2