yennanliu Add a LeetCode solution
Turn an LC number (plus, usually, a draft the user already wrote) into a committed-quality solution file and its README row, in the shape the other ~826 Python files already use.
Invocation: /lc-add <LC number> <pattern dir> — e.g. /lc-add 4038 Hash_table.
A reference or draft solution pasted under the command is used as V0; with no draft, the
draft is usually already in the contest scratch file (step 1).
Missing arguments are inferred, not asked about: the pattern dir from the technique the solution actually uses, the language from where the draft came from (default Python). Ask only if the number itself is missing or the dir is genuinely ambiguous.
Prime directives
- The problem page is the authority on the title; the class name is not. LC 4038's
method is
countSpecialIntegersand its problem is Count Integers Appearing in a Single Block. A slug guessed from a method name lands on the wrong file name and a dead README link. - Copy a neighbour, never invent the layout. Every file in a pattern dir has the same shape. Read one from the target dir before writing.
- The user's approach is the solution. When a draft is pasted, fix its bugs and keep
its idea as
V0. Replacing it with a cleverer one teaches nothing and hides the bug they wanted found. - Untested is unfinished. Run the docstring's own examples before reporting done.
- Say what was assumed. Difficulty inferred from contest position, examples written from the rule rather than copied from LC — state it, so it can be corrected.
The steps
1. Find the problem's source of truth
For a contest problem it is leetcode_python/lc_weekly/weekly_<n>/ws.txt — it records the
LC number, the problem URL, the user's idea notes and their draft (often with the bug they
hit, then a (fixed) version below it):
grep -rn "LC <number>" leetcode_python/lc_weekly/*/ws.txt
sed -n '/# LC <number>/,/^# LC /p' leetcode_python/lc_weekly/weekly_<n>/ws.txt
Two things to read out of it:
- The URL slug is the file name —
count-integers-appearing-in-a-single-block. - Position implies difficulty. The LC numbers appear in contest order, so the first is Q1 (Easy), then Medium, Medium/Hard, Hard. Mark it as an assumption in the report.
If the user pasted a URL or a full problem statement instead, that is the source of truth and this step is already done.
2. Read a neighbour before writing
ls leetcode_python/<Pattern_Dir>/
git log --oneline -12 --name-only # the last few files added, in any dir
Open one recent file from the target dir and match it. The layout below is the current house shape, but the dir wins if it has drifted.
3. Write leetcode_python/<Pattern_Dir>/<slug>.py
"""
<number>. <Exact Problem Title>
<Difficulty>
<the statement, as prose — wrapped, not one long line>
Example 1:
Input: nums = [1,1,2,2,3]
Output: 3
Explanation:
<why>
Constraints:
1 <= nums.length <= 10^5
"""
# V0
# IDEA : <ONE LINE — THE TECHNIQUE, IN CAPS LIKE ITS NEIGHBOURS>
#
# <2-6 indented lines saying WHY the trick is correct — the invariant, not a
# restatement of the loop. A worked mini-example earns its place here:>
#
# e.g. nums = [1,2,1] -> idx of 1 = [0,2] -> 2 - 0 + 1 = 3 != 2 -> NOT special
#
# time = O(n), space = O(n)
from collections import defaultdict
class Solution(object):
def <lcMethodName>(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
# edge
if not nums:
return 0
...
Rules that are not negotiable:
- The docstring block is first, before any import.
# V0is the canonical solution.# IDEA : ...header, indented why, then# time = O(...), space = O(...)as the last comment line before the code.- LeetCode's
:type: / :rtype:docstring stays on the method — these files are pasted back into LC. # NOTE !!!marks the one line a reader would get wrong. Use it once, not five times.- Python 2-style
class Solution(object)— it is what the whole tree uses.
4. A second variant needs a stated reason
One canonical solution per problem. A second one is justified only by a different
complexity, a distinct trick, or a different language idiom — not a different spelling of
the same loop. When justified it is # V0-1 (a variation on V0) or # V1 (a genuinely
different approach), each with its own IDEA and time = line, and the class is named
Solution2 / Solution3 so the file still imports.
5. Smoke-test before reporting done
The file name has dashes, so it is not importable — load it by path and run the docstring's examples plus the edges (empty, single element, all-same):
python3 -c "
import importlib.util
spec = importlib.util.spec_from_file_location('m', 'leetcode_python/<Dir>/<slug>.py')
m = importlib.util.module_from_spec(spec); spec.loader.exec_module(m)
s = m.Solution()
print([s.<method>(x) for x in ([1,1,2,2,3], [1,2,1], [5], [])])"
Every variant gets the same call, and they must agree. If an example from the problem statement disagrees, the solution is wrong — say so rather than adjusting the example.
6. Add the README row
Find the pattern's table and insert in ascending LC-number order (a 4-digit contest problem goes at the end of that table):
grep -n "leetcode_python/<Pattern_Dir>" README.md | tail -5
| <num> | [<Title>](<leetcode url>) | [Python](./leetcode_python/<Dir>/<slug>.py) | _O(t)_ | _O(s)_ | <Difficulty> | **<pattern>**, <tags>, LC weekly | AGAIN(1) |
- Match the spacing of the rows already there.
git show <sha> -- README.mdon a previousupdate <NNN> pycommit shows the exact column shape. - Add a second
Javalink into the same cell only if that file exists underleetcode_java/— check, do not assume the pair. - Tags: the pattern in bold first, then the trick worth grepping for later
(
hashmap,prefix sum,span == cnt trick), thenLC weeklyfor a contest problem, then company tags in backticks if known. - Status column:
AGAIN(1)for a first pass. Never downgrade a status the user has set.
7. Report what was assumed
Close with the file, the README line number, the test results, and every inference:
difficulty from contest position, examples written from the rule because ws.txt kept only
the statement, a Java link deliberately omitted.
Do not
- ❌ invent the file layout — copy a neighbour (step 2)
- ❌ guess the slug from the method name (step 1)
- ❌ hand back untested code (step 5)
- ❌ rewrite the user's approach into your own
- ❌ touch
data/progress.txt— the practice log is the user's own record and gets its own commit - ❌ commit or push unless asked
Worked example
lc-add 4038 Hash_table, with the user's draft pasted:
| Step | What it produced |
|---|---|
| 1 | weekly_517/ws.txt → slug count-integers-appearing-in-a-single-block, first of 4038/4039/4040/4041 → Easy |
| 2 | read count-special-triplets.py from the same dir |
| 3 | wrote the file; IDEA explains why last - first + 1 == count is the contiguity test |
| 4 | added V0-1 (keep only first/last/cnt) — justified: O(distinct) space, not O(n) cells |
| 5 | [1,1,2,2,3]→3, [1,2,1]→1, [5]→1, [1,2,1,3,3,2]→1, []→0, both variants agreeing |
| 6 | README row inserted after LC 4007, the last row of the hash-table table |
| 7 | flagged: difficulty inferred from contest position, examples written from the rule |