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/

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