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Editorial: Find the Balance Index

by admin ·

4

1 Intuition

If you know the total, the right sum at index i is total - left - nums[i].

2 Approach

Compute the total once, then scan left to right maintaining the left sum and check the balance condition at each index.

3 Complexity Analysis

Time O(n), Space O(1).

4 Solution Code 

class Solution:
    def pivotIndex(self, nums: list[int]) -> int:
        total, left = sum(nums), 0
        for i, x in enumerate(nums):
            if left == total - left - x:
                return i
            left += x
        return -1

5 Code Walkthrough

The reference solution below implements the approach step by step.