What is the time complexity of Find Words Containing Character?

The optimal solution has a time complexity of O(n*m).

What data structures are used to solve Find Words Containing Character?

This problem uses Array, String. Understanding these concepts is essential for solving this Easy problem efficiently.

What are the key insights for solving Find Words Containing Character?

Insight 1: The problem involves iterating through each word in the input array and checking if a specific character exists within that word. Insight 2: A simple linear scan of each word is sufficient to solve this problem. No complex data structures are needed.

Which companies ask LeetCode 2942. Find Words Containing Character in interviews?

This problem is frequently asked at Deliveroo.

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Find Words Containing Character - LeetCode 2942 Solution

Find Words Containing Character - Complete Solution Guide

Find Words Containing Character is LeetCode problem 2942, a Easy level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

You are given a 0-indexed array of strings words and a character x . Return an array of indices representing the words that contain the character x . Note that the returned array may be in any order. Example 1: Input: words = ["leet","code"], x = "e" Output: [0,1] Explanation: "e" occurs in both words: "l ee t", and "cod e ". Hence, we return indices 0 and 1. Example 2: Input: words = ["abc","bcd","aaaa","cbc"], x = "a" Output: [0,2] Explanation: "a" occurs in " a bc", and " aaaa ". Hence, we re

Detailed Explanation

The problem asks you to find all words in a given array of strings that contain a specific character. The input is a list of strings (words) and a single character (x). The output is a list of indices, where each index corresponds to a word in the input array that contains the character x. The order of indices in the output doesn't matter. For example, if the input words are ['leet', 'code'] and x is 'e', the output should be [0, 1] because 'e' is present in both words at indices 0 and 1.

Solution Approach

The provided solutions all employ a straightforward iterative approach. They iterate through each word in the input array. For each word, they check if the target character 'x' is present. If it is, the index of that word is added to the result list. This approach directly addresses the problem's requirement of finding and returning the indices of words containing the character.

Step-by-Step Algorithm

Step 1: Initialize an empty list (or array) called `result` to store the indices of words containing the character 'x'.
Step 2: Iterate through the input array `words` using a loop. The loop variable will keep track of the index of each word.
Step 3: Inside the loop, check if the character 'x' is present in the current word using an appropriate string function (e.g., `in` in Python, `indexOf` in Java, `find` in C++, manual character comparison in C).
Step 4: If the character 'x' is found in the current word, add the index of the word (the loop variable) to the `result` list.
Step 5: After iterating through all words, return the `result` list.

Key Insights

Insight 1: The problem involves iterating through each word in the input array and checking if a specific character exists within that word.
Insight 2: A simple linear scan of each word is sufficient to solve this problem. No complex data structures are needed.
Insight 3: The `in` operator (Python), `indexOf` (Java), `find` (C++), or a manual character-by-character search (C) efficiently checks for character presence in each string.

Complexity Analysis

Time Complexity: O(n*m)

Space Complexity: O(n)

Topics

This problem involves: Array, String.

Companies

Asked at: Deliveroo.

Find Words Containing Character | LeetCode 2942

Easy

Array String

Time: O(n*m)Space: O(n)

Solution Code

Available in:

import java.util.*;
class Solution {
    public List<Integer> findWordsContaining(String[] words, char x) {
        List<Integer> result = new ArrayList<>();
        for (int i = 0; i < words.length; i++) {
            if (words[i].indexOf(x) != -1) {
                result.add(i);
            }
        }
        return result;
    }
}

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Problem Info

Description

Problem 2942: Find Words Containing Character - Detailed explanation and solution approaches.

Topics

Array String

Companies

Deliveroo

Stats

Difficulty:Easy

Languages:4

Companies:1

Problem #:2942

Problem Explanation

💡

Think Before You Code

🤔 Ask Yourself

→What is the input? What output do I need?
→Can I solve a smaller version of this problem first?
→What patterns have I seen in similar problems?

✏️ Try This First

Before looking at the solution, try to solve it on paper with a simple example!

🚀 Try on LeetCode

Solution Approach

📋

Step-by-Step Solution

5 steps

1
Step 1: Initialize an empty list (or array) called `result` to store the indices of words containing the character 'x'.
2
Step 2: Iterate through the input array `words` using a loop. The loop variable will keep track of the index of each word.
3
Step 3: Inside the loop, check if the character 'x' is present in the current word using an appropriate string function (e.g., `in` in Python, `indexOf` in Java, `find` in C++, manual character comparison in C).
4
Step 4: If the character 'x' is found in the current word, add the index of the word (the loop variable) to the `result` list.
5
Step 5: After iterating through all words, return the `result` list.

💡

Pro Tip for Students

Try tracing through each step with a small example on paper before coding. Understanding "why" each step happens is more important than memorizing the code!

⚡

Complexity Analysis

⏱️

Time Complexity

O(n*m)

💾

Space Complexity

O(n)

📦 Linear space - Memory grows with input size.

📝

Why?

The time complexity comes from iterating through each of the n words. For each word, the algorithm performs a search operation which takes O(m) time in the worst case (character-by-character comparison). The space complexity comes from storing the indices of the words that contain the character x; in the worst case, all words might contain x, resulting in a list of size n.

📖New to Big O? Click to learn more

Big O Notation - Quick Guide

O(1)Best - Instant

O(log n)Excellent - Binary Search

O(n)Good - One loop

O(n log n)OK - Sorting

O(n²)Slow - Nested loops

O(2ⁿ)Very Slow - Recursion

Alternative Approaches

Using Regular Expressions

Regular expressions could be used to search for the character within each string. This approach might be less efficient for this specific problem but offers flexibility for more complex pattern matching.

Time: O(n*m) (likely similar to the linear scan)Space: O(n) (to store results)

Trade-offs: Regular expressions add overhead; the linear scan is simpler and more efficient for this specific problem. Regular expressions become beneficial when dealing with more sophisticated patterns.

✨

Key Insights

1Insight 1: The problem involves iterating through each word in the input array and checking if a specific character exists within that word.
2Insight 2: A simple linear scan of each word is sufficient to solve this problem. No complex data structures are needed.
3Insight 3: The `in` operator (Python), `indexOf` (Java), `find` (C++), or a manual character-by-character search (C) efficiently checks for character presence in each string.

📚

Key Terms Explained

For Students

Array

A collection of items stored at contiguous memory locations. Like a row of boxes.

String

A sequence of characters. Like a word or sentence in programming!

Edge Cases

Edge case 1: Empty input array `words`. The solution correctly handles this by returning an empty result list.
Edge case 2: No word contains the character 'x'. The solution correctly handles this by returning an empty result list.
Edge case 3: A word contains the character 'x' multiple times. The solution correctly adds the index only once.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Forgetting to handle the case where the character 'x' is not found in any of the words. The solution should return an empty list in this scenario.

✗Common mistake 2: Incorrectly managing indices in the result list. The index added to the result should correspond to the index of the word in the input array, not the index of the character within the word.

✗Common mistake 3: Inefficient character searching (e.g., using nested loops in C without optimization).

✅

Learning Tip

Every mistake is a learning opportunity! When you make an error, understand why it happened before moving on.

🌍

Where is This Used in Real Life?

💼Real-world scenario 1: Searching for specific keywords or characters in a log file to identify errors or events.

🏦Real-world scenario 2: Text processing applications where you need to filter or categorize text based on the presence of specific characters or words.

🎮Real-world scenario 3: Data validation: Checking if a field in a dataset contains a required character (e.g., '@' in email addresses).

💡Understanding real-world applications helps you see the "why" behind algorithms. It's not just about passing interviews—these concepts power the apps and websites you use every day!

Author's Notes

💡 Key Insight

When dealing with arrays, always consider if sorting would simplify the problem. Many array problems have O(n) solutions using hash maps or two-pointer technique.

🎯 Interview Tip

Don't rush. Explain your thought process clearly. Easy problems are often about communication.

⚠️ Watch Out

Off-by-one errors are the most common mistake. Double-check your loop bounds and array indices.

Written by Saswata Mondal

Software Engineer • Algorithms Enthusiast • Interview Coach

👨‍💻

About the Author

👨‍💻

Saswata MondalAuthor400+ LC Problems

B.Tech CSE, IEM Kolkata | LeetCode Rating: 1672 (Top 15%)

Certified: IBM Java Developer, NPTEL Programming in Java

Last updated: August 2, 2024LeetCode Profile GitHub

This solution has been crafted based on my experience solving 400+ LeetCode problems. Each explanation is designed to help you understand the underlying concepts, not just memorize the code.

Community Tips & Insights

I was asked this exact problem at my Google interview. The interviewer wanted me to optimize space complexity.

@InterviewProJul 14

Try solving this without using extra space first. It's a great exercise for understanding the underlying pattern.

@CodeNinjaJul 7

❓

Frequently Asked Questions

What is the most efficient way to solve array problems?

Most array problems can be solved efficiently using techniques like two-pointer approach, sliding window, or hash maps. The key is identifying whether the array is sorted (enabling binary search) or if tracking seen elements (using hash maps) can help achieve O(n) time complexity.

How do I handle string manipulation efficiently?

In languages with immutable strings (Java, Python, C#), use StringBuilder/list to avoid O(n) concatenation cost. Consider using character arrays for in-place modifications. For pattern matching, consider KMP or Rabin-Karp for O(n+m) complexity.

How should I approach easy-level algorithm problems?

Easy problems build foundational skills. Focus on: 1) Understanding the problem completely before coding, 2) Writing clean, readable code, 3) Handling all edge cases (empty input, single element, etc.), 4) Analyzing time and space complexity. Don't skip complexity analysis even for simple solutions.

How should I practice algorithm problems effectively?

Focus on understanding patterns rather than memorizing solutions. After solving a problem, review optimal solutions and understand the intuition. Group similar problems to recognize patterns. Practice explaining your approach out loud. Review problems after a few days to test retention.

What is the optimal approach for "Find Words Containing Character"?

For this easy-level Array problem, the key is to identify the core pattern. Analyze the input constraints to determine acceptable time complexity. Consider whether string techniques can optimize the solution. Always handle edge cases and validate your approach with examples before coding.

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