EasyNo. 2047
Number of Valid Words in a Sentence — LeetCode 2047 Python Solution
- Pattern
- Hash Map
- Topics
- String
- Reading time
- 3 min
- Source
- leetcode.com
The problem
A sentence consists of lowercase letters ('a' to 'z'), digits ('0' to '9'), hyphens ('-'), punctuation marks ('!', '.', and ','), and spaces (' ') only. Each sentence can be broken down into one or more tokens separated by one or more spaces ' '.
Example
- Input
- sentence = "cat and dog"
- Output
- 3
- Explanation
- The valid words in the sentence are "cat", "and", and "dog".
Python solution
class Solution:
def countValidWords(self, sentence: str) -> int:
def check(s: str) -> bool:
st = False
for i, c in enumerate(s):
if c.isdigit() or (c in "!.," and i < len(s) - 1):
return False
if c == "-":
if (
st
or i in (0, len(s) - 1)
or not s[i - 1].isalpha()
or not s[i + 1].isalpha()
):
return False
st = True
return True
return sum(check(s) for s in sentence.split())Complexity
- Time
- O(n)
- Space · auxiliary
- O(n)
Pattern: Hash Map
Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 2047. Number of Valid Words in a Sentence is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.
The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.
Related problems
| No. | Problem | Difficulty |
|---|---|---|
| 2042 | Check if Numbers Are Ascending in a Sentence | Easy |
| 0006 | Zigzag Conversion | Medium |
| 0008 | String to Integer (atoi) | Medium |
| 0038 | Count and Say | Medium |
| 0058 | Length of Last Word | Easy |
| 0065 | Valid Number | Hard |
Frequently asked questions
- How hard is LeetCode 2047. Number of Valid Words in a Sentence?
LeetCode 2047. Number of Valid Words in a Sentence is rated Easy on LeetCode.
- What is the time complexity of LeetCode 2047. Number of Valid Words in a Sentence?
The Python solution on this page runs in O(n).
- What is the space complexity of LeetCode 2047. Number of Valid Words in a Sentence?
The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 2047. Number of Valid Words in a Sentence cover?
LeetCode 2047. Number of Valid Words in a Sentence is tagged String on LeetCode.