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# 1991. Find the Middle Index in Array

<https://leetcode.com/problems/find-the-middle-index-in-array>

## Description

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.
```

**Example 4:**

```
**Input:** nums = [1]
**Output:** 0
**Explantion:**
The sum of the numbers before index 0 is: 0
The sum of the numbers after index 0 is: 0
```

**Constraints:**

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

**Note:** This question is the same as 724: <https://leetcode.com/problems/find-pivot-index/>

## ac

```java
```