Finding equilibrium index
Detailed guide and Python implementation for the 'Finding equilibrium index' problem.
Problem Statement
Write a function equilibrium_index(arr) that finds the equilibrium index of the array. An equilibrium index is an index i where the sum of elements at indices less than i equals the sum of elements at indices greater than i. Return the first equilibrium index found, or -1 if none exists. The element at index i is not included in either sum.
- •1 <= len(arr) <= 10^5
- •-10^9 <= arr[i] <= 10^9
Examples
arr = [-7, 1, 5, 2, -4, 3, 0]
3
At index 3: left sum = -7+1+5 = -1, right sum = -4+3+0 = -1. Both sums are equal.
arr = [1, 2, 3]
-1
No index satisfies the equilibrium condition.
arr = [1, 3, 5, 2, 2]
2
At index 2: left sum = 1+3 = 4, right sum = 2+2 = 4. Equal.
Need a Hint?
Edge Cases to Watch
- Empty input structures
- Single element inputs
- Large numerical bounds
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