参考：http://stackoverflow.com/questions/34584416/nested-loops-with-arrays
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.
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.
Example Tests:
1 Test.describe("FindEvenIndex", function() { 2 Test.it("Tests", function() { 3 Test.assertEquals(findEvenIndex([1,2,3,4,3,2,1]),3, "The array was: [1,2,3,4,3,2,1] "); 4 Test.assertEquals(findEvenIndex([1,100,50,-51,1,1]),1, "The array was: [1,100,50,-51,1,1] "); 5 Test.assertEquals(findEvenIndex([1,2,3,4,5,6]),-1, "The array was: [1,2,3,4,5,6] "); 6 Test.assertEquals(findEvenIndex([20,10,30,10,10,15,35]),3, "The array was: [20,10,30,10,10,15,35] "); 7 }); 8 });
Solution:
1 function findEvenIndex(arr) { 2 var add = (a, b) => a + b; 3 var sum = a => a.reduce(add, 0); 4 var isEven = (e, i, a) => sum(a.slice(0, i)) === sum(a.slice(i+1)); 5 6 return arr.findIndex(isEven); 7 }