1991. Find the Middle Index in Array

 Given a 0-indexed integer array nums, find the leftmost middleIndex (i.e., the smallest amongst all the possible ones).

A middleIndex is an index where nums[0] + nums[1] + ... + nums[middleIndex-1] == nums[middleIndex+1] + nums[middleIndex+2] + ... + nums[nums.length-1].

If middleIndex == 0, the left side sum is considered to be 0. Similarly, if middleIndex == nums.length - 1, the right side sum is considered to be 0.

Return the leftmost middleIndex that satisfies the condition, or -1 if there is no such index.

 

Example 1:

Input: nums = [2,3,-1,8,4]
Output: 3
Explanation: The sum of the numbers before index 3 is: 2 + 3 + -1 = 4
The sum of the numbers after index 3 is: 4 = 4

Example 2:

Input: nums = [1,-1,4]
Output: 2
Explanation: The sum of the numbers before index 2 is: 1 + -1 = 0
The sum of the numbers after index 2 is: 0

Example 3:

Input: nums = [2,5]
Output: -1
Explanation: There is no valid middleIndex.

 

Constraints:

• 1 <= nums.length <= 100
• -1000 <= nums[i] <= 1000

Soluation:

In JS:

var findMiddleIndex = function(nums) {

    let left=0;

    let sum=0;

    for(let i=0;i<nums.length;i++)

    {

      sum+=nums[i];

    }

    let sumleft = 0;

    for(let i=0; i<nums.length; i++){

        let sumright = sum - sumleft - nums[i];

        if(sumleft == sumright){

            return i;

        }

        sumleft += nums[i]; 

    }

    return -1;

};