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 a 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

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