What is the time complexity of Truncate Sentence?

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

What data structures are used to solve Truncate Sentence?

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

What are the key insights for solving Truncate Sentence?

Insight 1: The sentence can be easily split into words using the `split()` method (or equivalent in other languages). Insight 2: Slicing (or array indexing) allows direct access to the first `k` words after splitting.

Which companies ask LeetCode 1816. Truncate Sentence in interviews?

This problem is frequently asked at Accenture.

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Truncate Sentence - LeetCode 1816 Solution

Truncate Sentence - Complete Solution Guide

Truncate Sentence is LeetCode problem 1816, 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

A sentence is a list of words that are separated by a single space with no leading or trailing spaces. Each of the words consists of only uppercase and lowercase English letters (no punctuation). For example, "Hello World" , "HELLO" , and "hello world hello world" are all sentences. You are given a sentence s and an integer k . You want to truncate s such that it contains only the first k words. Return s after truncating it. Example 1: Input: s = "Hello how are

Detailed Explanation

The problem asks you to truncate a given sentence (a string of words separated by spaces) to keep only the first `k` words. The input is a sentence `s` and an integer `k` representing the number of words to keep. The output is the truncated sentence. The sentence contains only uppercase and lowercase English letters and spaces, with no leading or trailing spaces. The problem guarantees that `k` will always be within the valid range of the number of words in the sentence.

Solution Approach

The solutions provided utilize a straightforward approach. They first split the input sentence `s` into an array (or list) of words using the space character as a delimiter. Then, they select the first `k` words from this array. Finally, they join these `k` words back into a string, separated by spaces, to form the truncated sentence.

Step-by-Step Algorithm

Step 1: Split the input sentence `s` into an array of words using the space character as the delimiter.
Step 2: Select the first `k` words from the array (using array slicing or indexing).
Step 3: Join the selected `k` words back into a single string, using a space character as the separator.

Key Insights

Insight 1: The sentence can be easily split into words using the `split()` method (or equivalent in other languages).
Insight 2: Slicing (or array indexing) allows direct access to the first `k` words after splitting.
Insight 3: Efficient string manipulation is key; avoid unnecessary iterations if possible. Using built-in functions like `join` is often more efficient than manual string concatenation.

Complexity Analysis

Time Complexity: O(n)

Space Complexity: O(n)

Topics

This problem involves: Array, String.

Companies

Asked at: Accenture.

Truncate Sentence | LeetCode 1816

Easy

Array String

Time: O(n)Space: O(n)

Solution Code

Available in:

class Solution {
    public String truncateSentence(String s, int k) {
        String[] words = s.split(" ");
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < k; i++) {
            sb.append(words[i]);
            if (i < k - 1) {
                sb.append(" ");
            }
        }
        return sb.toString();
    }
}

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Problem Info

Description

Problem 1816: Truncate Sentence - Detailed explanation and solution approaches.

Topics

Array String

Companies

Accenture

Stats

Difficulty:Easy

Languages:4

Companies:1

Problem #:1816

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

3 steps

1
Step 1: Split the input sentence `s` into an array of words using the space character as the delimiter.
2
Step 2: Select the first `k` words from the array (using array slicing or indexing).
3
Step 3: Join the selected `k` words back into a single string, using a space character as the separator.

💡

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)

👍 Linear - Good! Visits each element once.

💾

Space Complexity

O(n)

📦 Linear space - Memory grows with input size.

📝

Why?

Splitting the string takes O(n) time in the worst case (all characters are spaces). Slicing the array takes O(k) time, where k is much less than n (k ≤ n). Joining the words takes O(n) time in the worst case. Overall, the dominant factor is O(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

In-place Modification (C-style)

The C solution modifies the original string directly by adding a null terminator after the k-th word. This avoids the need for creating a new string.

Time: O(n)Space: O(1)

Trade-offs: It modifies the input string, which might not be desirable in all cases. It's generally less readable and harder to maintain compared to the other solutions.

Manual Word Extraction

Iterate through the string character by character, counting words and building the truncated sentence. This avoids using the `split()` function but adds complexity.

Time: O(n)Space: O(n)

Trade-offs: Avoids the `split()` function but is less concise and potentially less efficient due to manual string manipulation.

✨

Key Insights

1Insight 1: The sentence can be easily split into words using the `split()` method (or equivalent in other languages).
2Insight 2: Slicing (or array indexing) allows direct access to the first `k` words after splitting.
3Insight 3: Efficient string manipulation is key; avoid unnecessary iterations if possible. Using built-in functions like `join` is often more efficient than manual string concatenation.

📚

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: `k` is equal to the number of words in the sentence. The solution should return the original sentence. All solutions handle this correctly.
Edge case 2: The sentence contains only one word. The solution should return the original sentence. All solutions handle this correctly.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Incorrectly handling the space between words when joining the truncated words. Forgetting to check the edge case of a single word or k being equal to the number of words.

✗Common mistake 2: Not handling the case where `k` is greater than the number of words in the sentence (though the problem statement guarantees this won't happen).

✅

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: Displaying short previews of text in user interfaces (e.g., search results, news feeds).

🏦Real-world scenario 2: Data processing tasks involving the extraction of key information from large text files where only a limited number of words are needed.

💡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

Use this problem to demonstrate clean code practices. Variable naming and code organization matter.

⚠️ 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: June 17, 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

The key insight here is recognizing the pattern. Once you see it, the solution becomes straightforward.

@AlgoMasterJul 13

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

@InterviewProJul 6

❓

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 "Truncate Sentence"?

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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