Find Pivot Index

Given an array of integers nums, calculate the pivot index of this array. The pivot index is the index where the sum of all numbers strictly to the left of the index equals the sum of all numbers strictly to the right. If no such index exists, return -1. If there are multiple pivot indices, return the left-most one.

Examples
Input: [1,7,3,6,5,6]
Output: 3
Hints

Find Pivot Index

Given an array of integers `nums`, calculate the pivot index of this array. The pivot index is the index where the sum of all numbers strictly to the left of the index equals the sum of all numbers strictly to the right. If no such index exists, return -1. If there are multiple pivot indices, return the left-most one.