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* added doctest for all_permutations.py * added doctest for all_subsequences.py * added doctest for all_subsequences.py * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * doctest added * updated * Update backtracking/all_subsequences.py --------- Co-authored-by: Harsh Buddhdev <harshbuddhdev5@.com> Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>
89 lines
2.5 KiB
Python
89 lines
2.5 KiB
Python
"""
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In this problem, we want to determine all possible permutations
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of the given sequence. We use backtracking to solve this problem.
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Time complexity: O(n! * n),
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where n denotes the length of the given sequence.
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"""
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from __future__ import annotations
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def generate_all_permutations(sequence: list[int | str]) -> None:
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create_state_space_tree(sequence, [], 0, [0 for i in range(len(sequence))])
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def create_state_space_tree(
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sequence: list[int | str],
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current_sequence: list[int | str],
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index: int,
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index_used: list[int],
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) -> None:
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"""
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Creates a state space tree to iterate through each branch using DFS.
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We know that each state has exactly len(sequence) - index children.
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It terminates when it reaches the end of the given sequence.
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:param sequence: The input sequence for which permutations are generated.
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:param current_sequence: The current permutation being built.
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:param index: The current index in the sequence.
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:param index_used: list to track which elements are used in permutation.
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Example 1:
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>>> sequence = [1, 2, 3]
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>>> current_sequence = []
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>>> index_used = [False, False, False]
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>>> create_state_space_tree(sequence, current_sequence, 0, index_used)
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[1, 2, 3]
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[1, 3, 2]
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[2, 1, 3]
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[2, 3, 1]
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[3, 1, 2]
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[3, 2, 1]
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Example 2:
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>>> sequence = ["A", "B", "C"]
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>>> current_sequence = []
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>>> index_used = [False, False, False]
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>>> create_state_space_tree(sequence, current_sequence, 0, index_used)
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['A', 'B', 'C']
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['A', 'C', 'B']
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['B', 'A', 'C']
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['B', 'C', 'A']
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['C', 'A', 'B']
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['C', 'B', 'A']
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Example 3:
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>>> sequence = [1]
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>>> current_sequence = []
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>>> index_used = [False]
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>>> create_state_space_tree(sequence, current_sequence, 0, index_used)
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[1]
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"""
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if index == len(sequence):
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print(current_sequence)
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return
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for i in range(len(sequence)):
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if not index_used[i]:
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current_sequence.append(sequence[i])
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index_used[i] = True
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create_state_space_tree(sequence, current_sequence, index + 1, index_used)
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current_sequence.pop()
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index_used[i] = False
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"""
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remove the comment to take an input from the user
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print("Enter the elements")
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sequence = list(map(int, input().split()))
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"""
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sequence: list[int | str] = [3, 1, 2, 4]
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generate_all_permutations(sequence)
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sequence_2: list[int | str] = ["A", "B", "C"]
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generate_all_permutations(sequence_2)
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