public class Solution
extends Object
1991 - Find the Middle Index in Array\.
Easy
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`
**Note:** This question is the same as 724