easyArraysPattern: Prefix Sum
Find Balance Index Solution
Problem Statement
You are given an array of integers `elements`. Find the index where the total sum of elements before it equals the total sum of elements after it. Return -1 if no such index exists.
Examples
Example 1:
Input:[1, 7, 3, 6, 5, 6]
Output:3
Explanation: Total deliveries before index 3 (1 + 7 + 3 = 11) equals total deliveries after index 3 (5 + 6 = 11)
Example 2:
Input:[1, 2, 3]
Output:-1
Explanation: No such index exists where total deliveries before it equals total deliveries after it
Constraints
- 1 <= n <= 10^4
- -1000 <= arr[i] <= 1000
Time: O(N) Space: O(1)
Use a single pass to calculate the total sum and then find the pivot index in O(n) time complexity
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