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112 lines
2.8 KiB
Python
112 lines
2.8 KiB
Python
"""
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Author : Alexander Pantyukhin
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Date : December 12, 2022
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Task:
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Given a string and a list of words, return true if the string can be
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segmented into a space-separated sequence of one or more words.
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Note that the same word may be reused
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multiple times in the segmentation.
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Implementation notes: Trie + Dynamic programming up -> down.
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The Trie will be used to store the words. It will be useful for scanning
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available words for the current position in the string.
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Leetcode:
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https://leetcode.com/problems/word-break/description/
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Runtime: O(n * n)
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Space: O(n)
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"""
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import functools
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from typing import Any
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def word_break(string: str, words: list[str]) -> bool:
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"""
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Return True if numbers have opposite signs False otherwise.
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>>> word_break("applepenapple", ["apple","pen"])
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True
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>>> word_break("catsandog", ["cats","dog","sand","and","cat"])
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False
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>>> word_break("cars", ["car","ca","rs"])
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True
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>>> word_break('abc', [])
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False
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>>> word_break(123, ['a'])
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Traceback (most recent call last):
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...
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ValueError: the string should be not empty string
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>>> word_break('', ['a'])
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Traceback (most recent call last):
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...
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ValueError: the string should be not empty string
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>>> word_break('abc', [123])
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Traceback (most recent call last):
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...
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ValueError: the words should be a list of non-empty strings
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>>> word_break('abc', [''])
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Traceback (most recent call last):
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...
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ValueError: the words should be a list of non-empty strings
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"""
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# Validation
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if not isinstance(string, str) or len(string) == 0:
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raise ValueError("the string should be not empty string")
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if not isinstance(words, list) or not all(
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isinstance(item, str) and len(item) > 0 for item in words
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):
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raise ValueError("the words should be a list of non-empty strings")
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# Build trie
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trie: dict[str, Any] = {}
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word_keeper_key = "WORD_KEEPER"
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for word in words:
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trie_node = trie
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for c in word:
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if c not in trie_node:
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trie_node[c] = {}
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trie_node = trie_node[c]
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trie_node[word_keeper_key] = True
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len_string = len(string)
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# Dynamic programming method
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@functools.cache
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def is_breakable(index: int) -> bool:
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"""
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>>> string = 'a'
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>>> is_breakable(1)
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True
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"""
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if index == len_string:
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return True
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trie_node = trie
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for i in range(index, len_string):
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trie_node = trie_node.get(string[i], None)
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if trie_node is None:
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return False
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if trie_node.get(word_keeper_key, False) and is_breakable(i + 1):
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return True
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return False
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return is_breakable(0)
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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