From d18eefa8ffe22cf99364c24e83a8a13bc20bc56e Mon Sep 17 00:00:00 2001 From: NeuroByte79 Date: Thu, 17 Sep 2026 22:56:36 +0530 Subject: [PATCH 1/3] Add edge cases for equilibrium index --- .../arrays/equilibrium_index_in_array.py | 65 ++++++++++++++----- 1 file changed, 50 insertions(+), 15 deletions(-) diff --git a/data_structures/arrays/equilibrium_index_in_array.py b/data_structures/arrays/equilibrium_index_in_array.py index 0717a45d9f4b..8950a8719888 100644 --- a/data_structures/arrays/equilibrium_index_in_array.py +++ b/data_structures/arrays/equilibrium_index_in_array.py @@ -1,52 +1,87 @@ + """ Find the Equilibrium Index of an Array. -Reference: https://www.geeksforgeeks.org/equilibrium-index-of-an-array/ -Python doctest can be run with the following command: +Reference: +https://www.geeksforgeeks.org/equilibrium-index-of-an-array/ + +Python doctest can be run with: + python -m doctest -v equilibrium_index_in_array.py -Given a sequence arr[] of size n, this function returns -an equilibrium index (if any) or -1 if no equilibrium index exists. +Given an array arr of size n, return an equilibrium index +if one exists, otherwise return -1. -The equilibrium index of an array is an index such that the sum of -elements at lower indexes is equal to the sum of elements at higher indexes. +An equilibrium index is an index where the sum of all +elements to the left equals the sum of all elements +to the right. +Examples: + >>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0]) + 3 -Example Input: -arr = [-7, 1, 5, 2, -4, 3, 0] -Output: 3 + >>> equilibrium_index([1, 2, 3, 4, 5]) + -1 + >>> equilibrium_index([1, 1, 1, 1, 1]) + 2 + + >>> equilibrium_index([2, 4, 6, 8, 10, 3]) + -1 """ def equilibrium_index(arr: list[int]) -> int: """ - Find the equilibrium index of an array. + Find the first equilibrium index of an array. Args: - arr (list[int]): The input array of integers. + arr: The input array of integers. Returns: - int: The equilibrium index or -1 if no equilibrium index exists. + The first equilibrium index, or -1 if none exists. Examples: + >>> equilibrium_index([]) + -1 + + >>> equilibrium_index([5]) + 0 + >>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0]) 3 + >>> equilibrium_index([1, 2, 3, 4, 5]) -1 + >>> equilibrium_index([1, 1, 1, 1, 1]) 2 - >>> equilibrium_index([2, 4, 6, 8, 10, 3]) - -1 + + >>> equilibrium_index([0, 0, 0]) + 0 + + >>> equilibrium_index([-1, -1, -1]) + 1 + + >>> equilibrium_index([1, -1, 0]) + 2 + + Time Complexity: + O(n), where n is the length of the array. + + Space Complexity: + O(1), using only constant extra space. """ total_sum = sum(arr) left_sum = 0 for i, value in enumerate(arr): total_sum -= value + if left_sum == total_sum: return i + left_sum += value return -1 @@ -55,4 +90,4 @@ def equilibrium_index(arr: list[int]) -> int: if __name__ == "__main__": import doctest - doctest.testmod() + doctest.testmod() \ No newline at end of file From dbfd526a94cfe071e5219f39fc9788d92542a89b Mon Sep 17 00:00:00 2001 From: "pre-commit-ci[bot]" <66853113+pre-commit-ci[bot]@users.noreply.github.com> Date: Thu, 17 Sep 2026 17:31:51 +0000 Subject: [PATCH 2/3] [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci --- data_structures/arrays/equilibrium_index_in_array.py | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/data_structures/arrays/equilibrium_index_in_array.py b/data_structures/arrays/equilibrium_index_in_array.py index 8950a8719888..897efa961f9c 100644 --- a/data_structures/arrays/equilibrium_index_in_array.py +++ b/data_structures/arrays/equilibrium_index_in_array.py @@ -1,4 +1,3 @@ - """ Find the Equilibrium Index of an Array. @@ -90,4 +89,4 @@ def equilibrium_index(arr: list[int]) -> int: if __name__ == "__main__": import doctest - doctest.testmod() \ No newline at end of file + doctest.testmod() From 8dc1f7c4220ba6b794a9334ba73065031012b63d Mon Sep 17 00:00:00 2001 From: Christian Clauss Date: Fri, 18 Sep 2026 00:57:35 +0200 Subject: [PATCH 3/3] Refactor docstring in equilibrium_index_in_array.py Updated docstring examples and formatting for clarity. --- .../arrays/equilibrium_index_in_array.py | 34 +++---------------- 1 file changed, 4 insertions(+), 30 deletions(-) diff --git a/data_structures/arrays/equilibrium_index_in_array.py b/data_structures/arrays/equilibrium_index_in_array.py index 897efa961f9c..dcb39959f8a7 100644 --- a/data_structures/arrays/equilibrium_index_in_array.py +++ b/data_structures/arrays/equilibrium_index_in_array.py @@ -2,67 +2,45 @@ Find the Equilibrium Index of an Array. Reference: -https://www.geeksforgeeks.org/equilibrium-index-of-an-array/ +https://www.geeksforgeeks.org/equilibrium-index-of-an-array Python doctest can be run with: python -m doctest -v equilibrium_index_in_array.py Given an array arr of size n, return an equilibrium index -if one exists, otherwise return -1. +if one exists; otherwise return -1. An equilibrium index is an index where the sum of all elements to the left equals the sum of all elements to the right. - -Examples: - - >>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0]) - 3 - - >>> equilibrium_index([1, 2, 3, 4, 5]) - -1 - - >>> equilibrium_index([1, 1, 1, 1, 1]) - 2 - - >>> equilibrium_index([2, 4, 6, 8, 10, 3]) - -1 """ def equilibrium_index(arr: list[int]) -> int: """ Find the first equilibrium index of an array. - Args: arr: The input array of integers. - Returns: The first equilibrium index, or -1 if none exists. - Examples: >>> equilibrium_index([]) -1 - >>> equilibrium_index([5]) 0 - >>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0]) 3 - + >>> equilibrium_index([2, 4, 6, 8, 10, 3]) + -1 >>> equilibrium_index([1, 2, 3, 4, 5]) -1 - >>> equilibrium_index([1, 1, 1, 1, 1]) 2 - >>> equilibrium_index([0, 0, 0]) 0 - >>> equilibrium_index([-1, -1, -1]) 1 - >>> equilibrium_index([1, -1, 0]) 2 @@ -74,15 +52,11 @@ def equilibrium_index(arr: list[int]) -> int: """ total_sum = sum(arr) left_sum = 0 - for i, value in enumerate(arr): total_sum -= value - if left_sum == total_sum: return i - left_sum += value - return -1