How hard is LeetCode 1181. Before and After Puzzle?

LeetCode 1181. Before and After Puzzle is rated Medium on LeetCode.

What is the time complexity of LeetCode 1181. Before and After Puzzle?

The Python solution on this page runs in O(n^2 \times m \times (\log n + \log m)).

What is the space complexity of LeetCode 1181. Before and After Puzzle?

The Python solution on this page uses O(n^2 \times m) auxiliary space.

What topics does LeetCode 1181. Before and After Puzzle cover?

LeetCode 1181. Before and After Puzzle is tagged Array, Hash Table, String and Sorting on LeetCode.

Is LeetCode 1181. Before and After Puzzle a premium problem?

Yes. LeetCode 1181. Before and After Puzzle is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.

MediumNo. 1181LeetCode Premium

Before and After Puzzle — LeetCode 1181 Python Solution

Pattern: Sorting
Topics: Array, Hash Table, String, Sorting
Reading time: 2 min
Source: leetcode.com

The problem

Given a list of phrases, generate a list of Before and After puzzles. A phrase is a string that consists of lowercase English letters and spaces only.

Python solution

PythonSolution

class Solution:
    def beforeAndAfterPuzzles(self, phrases: List[str]) -> List[str]:
        ps = []
        for p in phrases:
            ws = p.split()
            ps.append((ws[0], ws[-1]))
        n = len(ps)
        ans = []
        for i in range(n):
            for j in range(n):
                if i != j and ps[i][1] == ps[j][0]:
                    ans.append(phrases[i] + phrases[j][len(ps[j][0]) :])
        return sorted(set(ans))

Complexity

Time: O(n² × m × (log n + log m))
Space · auxiliary: O(n² × m)

Pattern: Sorting

Spend O(n log n) once to buy an ordering that makes the rest of the problem trivial. LeetCode 1181. Before and After Puzzle is filed here because LeetCode tags it Sorting, which is the vocabulary this hub collects.

The sorting guide has the Python template for the pattern and the 401 LeetCode problems that use it.

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Frequently asked questions

How hard is LeetCode 1181. Before and After Puzzle?: LeetCode 1181. Before and After Puzzle is rated Medium on LeetCode.
What is the time complexity of LeetCode 1181. Before and After Puzzle?: The Python solution on this page runs in O(n² × m × (log n + log m)).
What is the space complexity of LeetCode 1181. Before and After Puzzle?: The Python solution on this page uses O(n² × m) auxiliary space.
What topics does LeetCode 1181. Before and After Puzzle cover?: LeetCode 1181. Before and After Puzzle is tagged Array, Hash Table, String and Sorting on LeetCode.
Is LeetCode 1181. Before and After Puzzle a premium problem?: Yes. LeetCode 1181. Before and After Puzzle is a LeetCode Premium problem, so the full statement and test cases require a paid LeetCode subscription.

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python

Please analyze this context and help me answer the question or solve the problem.

Transcript

"Okay, next one. Given a string, return the length of the longest substring that has no repeating characters. Walk me through your approach before you code it."

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 Terra

Transcribing...

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python

Please analyze this context and help me answer the question or solve the problem.

Transcript

"Okay, next one. Given a string, return the length of the longest substring that has no repeating characters. Walk me through your approach before you code it."

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

Transcribing...

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

Transcript

"Okay, next one. Given a string, return the length of the longest substring that has no repeating characters. Walk me through your approach before you code it."

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

Transcribing...

Primary display

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

The problem

Python solution

Complexity

Pattern: Sorting

Related problems

Frequently asked questions

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Approach

Approach

Approach