6kyu Equal Sides Of An Array

Posted 2020-10-01 tong24

题目：

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.
An empty array should be treated like a 0 in this problem.

 

答案：

　　　　// 1

              function findEvenIndex (arr) {

                     function eleadd (x, y) {

                            return x + y;

                     }

 

                     var i;

                     for (var i = 1; i < arr.length - 1; i++) {

                            if (arr.slice(0, i).reduce(eleadd)) {

                                   return i;

                            }

                     }

                     return -1;

              }

 

              // 2

              function findEventIndex (arr) {

                     for (var i = 1; i < arr.length - 1; i++) {

                            if (arr.slice(0, i).reduce((a, b) => a + b) === arr.slice(i + 1).reduce((a, b) => a + b)) {

                                   return i;

                            }

                     }

                     return -1;

              }

 

              // 3

              function findEventIndex (arr) {

                     var left = 0, right = arr.reduce(function (pv, cv) {

                            return pv + cv;

                     }, 0);

                     for (var i = 0; i < arr.length; i++) {

                            if (i > 0) {

                                   left  += arr[i - 1];

                                   right -= arr[i];

                            }

                            if (left == right) {

                                   return i;

                            }

                     }

                     return -1;

              }