added rangeSum

Beginner/rangeSum/index-SOLUTION.js

@@ -0,0 +1,35 @@
+// USING A FOR LOOP
+function rangeSum(arr) {
+  let sum = 0;
+  for (i = arr[0]; i <= arr[1]; i++) {
+    sum += i;
+  }
+  return sum;
+}
+
+// USING THE ARITHMETIC PROGRESSION FORMULA
+function rangeSum(arr) {
+  let arrList = [];
+  for (i = arr[0]; i <= arr[1]; i++) {
+    arrList.push(i);
+  }
+  return (arrList.length * (arr[0] + arr[1])) / 2;
+}
+
+// USING RECURSION
+function rangeSum(arr) {
+  if (arr[0] == arr[1]) {
+    return arr[0];
+  } else {
+    return rangeSum([arr[0], arr[1] - 1]) + arr[1];
+  }
+}
+
+// USING .REDUCE()
+function rangeSum(arr) {
+  let arrList = [];
+  for (i = arr[0]; i <= arr[1]; i++) {
+    arrList.push(i);
+  }
+  return arrList.reduce((acc, num) => acc + num, 0);
+}

Beginner/rangeSum/index-START.js

@@ -0,0 +1,5 @@
+function rangeSum(arr) {
+  // Code goes here
+}
+
+module.exports = rangeSum;