Practice/Google/Leetcode 724. Find Pivot Index

Leetcode 724. Find Pivot Index

CodingMust

Problem

Given an array of integers, find the leftmost index where the sum of all elements strictly to the left of that index equals the sum of all elements strictly to the right of that index.

If no such index exists, return -1.

Elements "strictly to the left" means all elements with indices less than the current index. Elements "strictly to the right" means all elements with indices greater than the current index. The element at the index itself is not included in either sum.

Requirements

1. Return the smallest (leftmost) index that satisfies the balance condition
2. If multiple indices satisfy the condition, return the first one
3. Return -1 if no balance point exists
4. Handle arrays with negative numbers correctly

Constraints

• 1 ≤ nums.length ≤ 10⁴
• -1000 ≤ nums[i] ≤ 1000
• Time complexity should be O(n)
• Space complexity should be O(1)

Examples

Example 1:

` Input: nums = [1, 7, 3, 6, 5, 6] Output: 3 Explanation:

• At index 3 (value = 6):
  • Left sum = 1 + 7 + 3 = 11
  • Right sum = 5 + 6 = 11
  • They are equal, so return 3 `

Example 2:

` Input: nums = [5] Output: 0 Explanation:

• At index 0:
  • Left sum = 0 (no elements to the left)
  • Right sum = 0 (no elements to the right)
  • They are equal, so return 0 `

Example 3:

Input: nums = [1, 2, 3, 4] Output: -1 Explanation: No index satisfies the balance condition

Example 4:

` Input: nums = [2, 1, -1] Output: 0 Explanation:

• At index 0:
  • Left sum = 0
  • Right sum = 1 + (-1) = 0
  • They are equal, so return 0 `