Leetcode #1410: HTML Entity Parser
In this guide, we solve Leetcode #1410 HTML Entity Parser in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
HTML entity parser is the parser that takes HTML code as input and replace all the entities of the special characters by the characters itself. The special characters and their entities for HTML are: Quotation Mark: the entity is " and symbol character is ".
Quick Facts
- Difficulty: Medium
- Premium: No
- Tags: Hash Table, String
Intuition
Fast membership checks and value lookups are the heart of this problem, which makes a hash map the natural choice.
By storing what we have already seen (or counts/indexes), we can answer the question in one pass without backtracking.
Approach
Scan the input once, using the map to detect when the condition is satisfied and to update state as you go.
This keeps the solution linear while remaining easy to explain in an interview setting.
Steps:
- Initialize a hash map for seen items or counts.
- Iterate through the input, querying/updating the map.
- Return the first valid result or the final computed value.
Example
Input: text = "& is an HTML entity but &ambassador; is not."
Output: "& is an HTML entity but &ambassador; is not."
Explanation: The parser will replace the & entity by &
Python Solution
class Solution:
def entityParser(self, text: str) -> str:
d = {
'"': '"',
''': "'",
'&': "&",
">": '>',
"<": '<',
"⁄": '/',
}
i, n = 0, len(text)
ans = []
while i < n:
for l in range(1, 8):
j = i + l
if text[i:j] in d:
ans.append(d[text[i:j]])
i = j
break
else:
ans.append(text[i])
i += 1
return ''.join(ans)
Complexity
The time complexity is , and the space complexity is . The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.