What is the best approach to solve Find Pivot Index?

The optimal approach for Find Pivot Index is the "Optimal — Prefix Sum with Total" technique. It runs in O(n) time and uses O(1) space. Precompute total = sum(nums). Track leftSum as we iterate. At index i, rightSum = total - leftSum - nums[i]. Check if leftSum == rightSum. O(n) with a single pass.

What is the time complexity of Find Pivot Index?

The optimal solution for Find Pivot Index has a time complexity of O(n) and a space complexity of O(1), achieved using the Prefix Sum pattern.

Is Find Pivot Index a Easy LeetCode problem?

Yes, LeetCode #724 (Find Pivot Index) is rated Easy. It uses the Prefix Sum pattern and is commonly asked in interviews at Google, Amazon, Bloomberg.

How to solve Find Pivot Index in Python, Java, C++, and JavaScript?

LumiChats provides complete solutions for Find Pivot Index in Python, Java, C++, and JavaScript, along with step-by-step visual animations and time/space complexity analysis. All solutions are free to view.

#724EasyPrefix Sum

Find Pivot Index

Use total sum and running left sum to find where left equals right.

GoogleAmazonBloomberg

Problem Statement

Given an array nums, find the pivot index: the index where the sum of all numbers to the left equals the sum to the right. If no such index exists, return -1. If there are multiple, return the leftmost.

Examples

Example 1

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

Output:3

Explanation: Left sum = 1+7+3=11. Right sum = 5+6=11.

Example 2

Input:nums = [1,2,3]

Output:-1

Explanation: No pivot exists.

Constraints

1 ≤ nums.length ≤ 10⁴
-1000 ≤ nums[i] ≤ 1000

Solutions

Brute Force — Recompute sums

TimeO(n²)SpaceO(1)

For each index, compute left sum and right sum separately. O(n²) due to repeated summations.

Visual Animation

def pivotIndex(nums: list[int]) -> int:
    for i in range(len(nums)):
        if sum(nums[:i]) == sum(nums[i+1:]):
            return i
    return -1

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