public class Solution
extends Object
724 - Find Pivot Index\.
Easy
Given an array of integers `nums`, calculate the **pivot index** of this array.
The **pivot index** is the index where the sum of all the numbers **strictly** to the left of the index is equal to the sum of all the numbers **strictly** to the index's right.
If the index is on the left edge of the array, then the left sum is `0` because there are no elements to the left. This also applies to the right edge of the array.
Return _the **leftmost pivot index**_. If no such index exists, return -1.
**Example 1:**
**Input:** nums = [1,7,3,6,5,6]
**Output:** 3
**Explanation:**
The pivot index is 3.
Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11
Right sum = nums[4] + nums[5] = 5 + 6 = 11
**Example 2:**
**Input:** nums = [1,2,3]
**Output:** -1
**Explanation:**
There is no index that satisfies the conditions in the problem statement.
**Example 3:**
**Input:** nums = [2,1,-1]
**Output:** 0
**Explanation:**
The pivot index is 0.
Left sum = 0 (no elements to the left of index 0)
Right sum = nums[1] + nums[2] = 1 + -1 = 0
**Constraints:**
* 1 <= nums.length <= 104
* `-1000 <= nums[i] <= 1000`
**Note:** This question is the same as 1991: [https://leetcode.com/problems/find-the-middle-index-in-array/](https://leetcode.com/problems/find-the-middle-index-in-array/)