Implement function programming on q 149

Author: logreg-n-coffee

code/149-implement-sum.js

@@ -0,0 +1,25 @@
+/*
+Given a list of numbers L, 
+implement a method sum(i, j) which returns the sum from the sublist L[i:j] (including i, excluding j).
+
+For example, given L = [1, 2, 3, 4, 5], sum(1, 3) should return sum([2, 3]), which is 5.
+
+You can assume that you can do some pre-processing. 
+sum() should be optimized over the pre-processing step.
+ */
+
+(() => { 
+    Array.prototype.sum = function (startIndex, endIndex) {
+        endIndex = endIndex || this.length;
+
+        let sum = 0;
+        for (let i = startIndex; i < endIndex; i++) {
+            sum += this[i];
+        }
+        
+        return sum;
+    }
+
+    const l = [1, 2, 3, 4, 5];
+    console.log(l.sum(1, 3));
+})();

package.json

@@ -150,7 +150,8 @@
     "145": "nodemon --exec ts-node code/145-swap-every-two-nodes-linked-list.ts",
     "146": "nodemon --exec ts-node code/146-prune-a-tree.ts",
     "147": "nodemon --exec ts-node code/147-sort-a-list-using-reverse.ts",
-    "148": "nodemon --exec ts-node code/148-generate-gray-code.ts"
+    "148": "nodemon --exec ts-node code/148-generate-gray-code.ts",
+    "149": "nodemon --exec ts-node code/149-implement-sum.js"
   },
   "keywords": [],
   "author": "",