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

?presum 求解即可，只是沒想到會100%。。。。

Runtime:?0 ms, faster than?100.00%?of?Java?online submissions for?Find the Middle Index in Array.

Memory Usage:?41.3 MB, less than?33.54%?of?Java?online submissions for?Find the Middle Index in Array.