You are given a?0-indexed?integer array?nums?of length?n.

nums?contains a?valid split?at index?i?if the following are true:

• The sum of the first?i + 1?elements is?greater than or equal to?the sum of the last?n - i - 1?elements.

• There is?at least one?element to the right of?i. That is,?0 <= i < n - 1.

Return?the number of?valid splits?in?nums.

?

Example 1:

Input: nums = [10,4,-8,7]

Output: 2

Explanation: There are three ways of splitting nums into two non-empty parts:?

- Split nums at index 0.?

Then, the first part is [10], and its sum is 10.?

The second part is [4,-8,7], and its sum is 3.?

Since 10 >= 3, i = 0 is a valid split.?

- Split nums at index 1.?

Then, the first part is [10,4], and its sum is 14.?

The second part is [-8,7], and its sum is -1.?

Since 14 >= -1, i = 1 is a valid split.?

- Split nums at index 2. Then, the first part is [10,4,-8], and its sum is 6.?

The second part is [7], and its sum is 7. Since 6 < 7, i = 2 is not a valid split. Thus, the number of valid splits in nums is 2.

Example 2:

Input: nums = [2,3,1,0]

Output: 2

Explanation: There are two valid splits in nums:

- Split nums at index 1. Then, the first part is [2,3], and its sum is 5.?

The second part is [1,0], and its sum is 1.?

Since 5 >= 1, i = 1 is a valid split.?

- Split nums at index 2. Then, the first part is [2,3,1], and its sum is 6.?

The second part is [0], and its sum is 0. Since 6 >= 0, i = 2 is a valid split.

?

典型的pre_sum問(wèn)題，利用前綴和即可。

Constraints:

• 2 <= nums.length <= 105

• -105?<= nums[i] <= 105

Runtime:?4 ms, faster than?44.85%?of?Java?online submissions for?Number of Ways to Split Array.

Memory Usage:?59.8 MB, less than?23.68%?of?Java?online submissions for?Number of Ways to Split Array.