How hard is LeetCode 1002. Find Common Characters?

LeetCode 1002. Find Common Characters is rated Easy on LeetCode.

What is the time complexity of LeetCode 1002. Find Common Characters?

The Python solution on this page runs in O(n \sum w_i).

What is the space complexity of LeetCode 1002. Find Common Characters?

The Python solution on this page uses O(|\Sigma|) auxiliary space.

What topics does LeetCode 1002. Find Common Characters cover?

LeetCode 1002. Find Common Characters is tagged Array, Hash Table and String on LeetCode.

EasyNo. 1002

Find Common Characters — LeetCode 1002 Python Solution

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

The problem

Given a string array words, return an array of all characters that show up in all strings within the words (including duplicates). You may return the answer in any order.

Example

Input: words = ["bella","label","roller"]
Output: ["e","l","l"]

Python solution

PythonSolution

class Solution:
    def commonChars(self, words: List[str]) -> List[str]:
        cnt = Counter(words[0])
        for w in words:
            t = Counter(w)
            for c in cnt:
                cnt[c] = min(cnt[c], t[c])
        return list(cnt.elements())

Complexity

Time: O(n Σ w_i)
Space · auxiliary: O(|Σ|)

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 1002. Find Common Characters is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Hash Table.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

Related problems
No.	Problem	Difficulty
0049	Group Anagrams	Medium
0139	Word Break	Medium
0140	Word Break II	Hard
0336	Palindrome Pairs	Hard
0500	Keyboard Row	Easy
0522	Longest Uncommon Subsequence II	Medium

Frequently asked questions

How hard is LeetCode 1002. Find Common Characters?: LeetCode 1002. Find Common Characters is rated Easy on LeetCode.
What is the time complexity of LeetCode 1002. Find Common Characters?: The Python solution on this page runs in O(n Σ w_i).
What is the space complexity of LeetCode 1002. Find Common Characters?: The Python solution on this page uses O(|Σ|) auxiliary space.
What topics does LeetCode 1002. Find Common Characters cover?: LeetCode 1002. Find Common Characters is tagged Array, Hash Table and String on LeetCode.

Stuck on problems like this in a live interview?

Stealth Interview is a desktop app for macOS and Windows. It reads the problem off your screen and returns a working solution with a step-by-step explanation and its time and space complexity, invisible to screen sharing.

Download for Mac Download for Windows

Free to download. Check it runs on your machine, then pick a plan.

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."

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...

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...

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

Example

Python solution

Complexity

Pattern: Hash Map

Related problems

Frequently asked questions

Stuck on problems like this in a live interview?

Approach

Approach

Approach