Problem Statement

Given an integer array nums, determine the pivot index of this array.

The pivot index divides the array in such a way that the sum of the numbers on its left side is exactly equal to the sum of the numbers on its right side.

If the index is at the beginning, the sum to its left is considered zero, similarly for an index at the end.

Return the leftmost pivot index. If no such index exists, return -1.

Examples

• Example 1:

  • Input: [1, 2, 3, 4, 3, 2, 1]
  • Expected Output: 3
  • Justification: The sum of the numbers to the left of index 3 (1 + 2 + 3) is 6, and the sum to its right (3 + 2 + 1) is also 6.

• Example 2:

  • Input: [2, 1, 3]
  • Expected Output: -1
  • Justification: There is no pivot index that exists in the given array.

• Example 3:

  • Input: [1, 100, 50, -51, 1, 1]
  • Expected Output: 1
  • Justification: The sum to the left of index 1 is 1, and the sum to its right (50 + (-51) + 1 + 1) is 1.

Try it yourself

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