20. Find the Pivot Index

Given an integer array nums, find the leftmost pivot index — the index where the sum of all numbers strictly to its left equals the sum of all numbers strictly to its right. Return -1 if no such index exists.

Input: An integer array nums.

Output: Integer — leftmost pivot index, or -1.

Examples

Input: [1,7,3,6,5,6]
Output: 3
Explanation: Left of index 3: 1+7+3=11. Right of index 3: 5+6=11. Equal → return 3.

Input: [1,2,3]
Output: -1
Explanation: No index satisfies left_sum == right_sum → return -1.

Input: [2,1,-1]
Output: 0
Explanation: Left of 0: empty sum = 0. Right of 0: 1+(-1)=0. Equal → return 0.

Constraints

• 1 <= nums.length <= 10^4
• -1000 <= nums[i] <= 1000

Asked by