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59 lines
1.3 KiB
Python
59 lines
1.3 KiB
Python
"""
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Find the Equilibrium Index of an Array.
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Reference: https://www.geeksforgeeks.org/equilibrium-index-of-an-array/
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Python doctest can be run with the following command:
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python -m doctest -v equilibrium_index_in_array.py
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Given a sequence arr[] of size n, this function returns
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an equilibrium index (if any) or -1 if no equilibrium index exists.
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The equilibrium index of an array is an index such that the sum of
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elements at lower indexes is equal to the sum of elements at higher indexes.
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Example Input:
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arr = [-7, 1, 5, 2, -4, 3, 0]
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Output: 3
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"""
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def equilibrium_index(arr: list[int]) -> int:
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"""
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Find the equilibrium index of an array.
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Args:
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arr (list[int]): The input array of integers.
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Returns:
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int: The equilibrium index or -1 if no equilibrium index exists.
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Examples:
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>>> equilibrium_index([-7, 1, 5, 2, -4, 3, 0])
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3
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>>> equilibrium_index([1, 2, 3, 4, 5])
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-1
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>>> equilibrium_index([1, 1, 1, 1, 1])
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2
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>>> equilibrium_index([2, 4, 6, 8, 10, 3])
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-1
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"""
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total_sum = sum(arr)
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left_sum = 0
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for i, value in enumerate(arr):
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total_sum -= value
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if left_sum == total_sum:
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return i
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left_sum += value
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return -1
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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