Replace Words — LeetCode 648 Python Solution
MediumTrieArrayHash TableString
- Problem
- #648
- Pattern
- Trie
- Reading time
- 6 min
- Source
- leetcode.com
The problem
In English, we have a concept called root, which can be followed by some other word to form another longer word - let's call this word derivative. For example, when the root "help" is followed by the word "ful", we can form a derivative "helpful".
Example
- Input
- dictionary = ["cat","bat","rat"], sentence = "the cattle was rattled by the battery"
- Output
- "the cat was rat by the bat"
Python solution
Python
class Trie:
def __init__(self):
self.children: List[Trie | None] = [None] * 26
self.ref: int = -1
def insert(self, w: str, i: int):
node = self
for c in w:
idx = ord(c) - ord("a")
if node.children[idx] is None:
node.children[idx] = Trie()
node = node.children[idx]
node.ref = i
def search(self, w: str) -> int:
node = self
for c in w:
idx = ord(c) - ord("a")
if node.children[idx] is None:
return -1
node = node.children[idx]
if node.ref != -1:
return node.ref
return -1
class Solution:
def replaceWords(self, dictionary: List[str], sentence: str) -> str:
trie = Trie()
for i, w in enumerate(dictionary):
trie.insert(w, i)
ans = []
for w in sentence.split():
idx = trie.search(w)
ans.append(dictionary[idx] if idx != -1 else w)
return " ".join(ans)Complexity
| Measure | Complexity |
|---|---|
| Time | O(n) |
| Space | O(n) auxiliary |
Pattern: Trie
Store a set of words by their shared prefixes so lookups cost the length of the word. LeetCode 648. Replace Words is filed here because LeetCode tags it Trie, which is the vocabulary this hub collects.
The trie guide has the Python template for the pattern and the 49 LeetCode problems that use it.
Related problems
Frequently asked questions
- How hard is LeetCode 648. Replace Words?
- LeetCode 648. Replace Words is rated Medium on LeetCode.
- What is the time complexity of LeetCode 648. Replace Words?
- The Python solution on this page runs in O(n).
- What is the space complexity of LeetCode 648. Replace Words?
- The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 648. Replace Words cover?
- LeetCode 648. Replace Words is tagged Trie, Array, Hash Table and String on LeetCode.