adding find even idx

Author: abranhe

docs/find-even-index.md

@@ -0,0 +1,57 @@
+# find-even-index
+
+You are going to be given an array of integers. Your job is to take that array and find an index N where the sum of the integers to the left of N is equal to the sum of the integers to the right of N. If there is no index that would make this happen, return `-1`.
+
+### For example:
+
+Let's say you are given the array `{1,2,3,4,3,2,1}`:
+Your function will return the index `3`, because at the 3rd position of the array, the sum of left side of the index (`{1,2,3}`) and the sum of the right side of the index (`{3,2,1}`) both equal `6`.
+
+Let's look at another one.
+You are given the array `{1,100,50,-51,1,1}`:
+Your function will return the index 1, because at the 1st position of the array, the sum of left side of the index (`{1}`) and the sum of the right side of the index (`{50,-51,1,1}`) both equal `1`.
+
+### Last one:
+
+You are given the array `{20,10,-80,10,10,15,35}`
+At index `0` the left side is `{}`
+The right side is `{10,-80,10,10,15,35}`
+They both are equal to 0 when added. (Empty arrays are equal to 0 in this problem)
+Index `0` is the place where the left side and right side are equal.
+
+**Note:** Please remember that in most programming/scripting languages the index of an array starts at `0`.
+
+### Input:
+
+An integer array of length `0 < arr < 1000`. The numbers in the array can be any integer positive or negative.
+
+### Output:
+
+The lowest index N where the side to the left of N is equal to the side to the right of N. If you do not find an index that fits these rules, then you will return `-1`.
+
+**Note:**
+
+If you are given an array with multiple answers, return the lowest correct index.
+
+## Install
+
+```
+$ npm install @abranhe/codewars
+```
+
+## Usage
+
+```js
+const codewars = require('@abranhe/codewars');
+
+codewars.findEvenIndex([1, 2, 3, 4, 3, 2, 1]);
+//=> 3
+```
+
+## API
+
+### codewars.findEvenIndex(input)
+
+#### input
+
+Type: `array`

readme.md

@@ -30,6 +30,7 @@ codewars.maskify('454233223424324');
 - [codewars.squareDigit()](docs/square-every-digit.md)
 - [codewars.complementaryDNA()](docs/complementary-dna.md)
 - [codewars.getMiddle()](docs/middle-character.md)
+- [codewars.findEvenIndex()](docs/find-even-index.md)
 
 ## License
 

src/find-even-index.js

@@ -0,0 +1,5 @@
+module.exports = arr => {
+	return arr.findIndex((i, idx) => {
+		return arr.slice(0, idx).reduce((pv, cv) => pv + cv, 0) === arr.slice(idx + 1).reduce((pv, cv) => pv + cv, 0);
+	});
+};

src/index.js

@@ -5,11 +5,13 @@ const spinWords = require('./spin-words');
 const squareDigits = require('./square-every-digit');
 const complementaryDNA = require('./complementary-dna');
 const getMiddle = require('./middle-character');
+const findEvenIndex = require('./find-even-index');
 
 module.exports = {
 	maskify,
 	spinWords,
 	squareDigits,
 	complementaryDNA,
-	getMiddle
+	getMiddle,
+	findEvenIndex
 };

tests/find-even-index.test.js

@@ -0,0 +1,9 @@
+import test from 'ava';
+import {findEvenIndex} from '../src';
+
+test('Check find-even-index.js', t => {
+	t.is(findEvenIndex([1, 2, 3, 4, 3, 2, 1]), 3);
+	t.is(findEvenIndex([1, 100, 50, -51, 1, 1]), 1);
+	t.is(findEvenIndex([1, 2, 3, 4, 5, 6]), -1);
+	t.is(findEvenIndex([20, 10, 30, 10, 10, 15, 35]), 3);
+});