Truncate Sentence - Practice Coding Problems

Truncate Sentence - Problem

Array String Easy

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.

Input & Output

Example 1 — Basic Case

$ Input: s = "My dog ate his homework", k = 3

› Output: "My dog ate"

💡 Note: Take the first 3 words: "My", "dog", "ate". Join them with spaces to get "My dog ate".

Example 2 — Single Word

$ Input: s = "chomp chomp chomp", k = 1

› Output: "chomp"

💡 Note: Take only the first word "chomp" since k=1.

Example 3 — All Words

$ Input: s = "Hello world", k = 3

› Output: "Hello world"

💡 Note: k=3 but sentence only has 2 words, so return entire sentence "Hello world".

Constraints

1 ≤ s.length ≤ 500
k is a positive integer
1 ≤ k ≤ number of words in s
s consists of only lowercase and uppercase English letters and spaces

Visualization

Tap to expand

Understanding the Visualization

Input

Sentence string and target word count k

Process

Identify and select first k words

Output

Truncated sentence with exactly k words

Key Takeaway

🎯 Key Insight: Process only as many characters as needed to find k complete words

Asked in

a Amazon 25 M Microsoft 18

The key insight is to identify word boundaries and stop processing once we have k complete words. Best approach is split and join for simplicity: split by spaces, take first k elements, join back. Time: O(n), Space: O(n)

Common Approaches

Approach	Time	Space	Notes
✓ Split and Join Approach	O(n)	O(n)	Split sentence into words array, take first k words, join back
Brute Force - Character by Character	O(n)	O(1)	Iterate through each character, count spaces to track word boundaries

Split and Join Approach — Algorithm Steps

Split sentence by spaces into words array
Take first k words using array slicing
Join the selected words back with spaces

Visualization

Tap to expand

Step-by-Step Walkthrough

Split

Split sentence into individual words

Select

Take first k words from array

Join

Combine selected words back with spaces

Code -

solution.c — C

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char* solution(char* s, int k) {
    int len = strlen(s);
    char* result = malloc(len + 1);
    strcpy(result, s);
    
    int wordCount = 0;
    int lastSpacePos = -1;
    
    for (int i = 0; i < len; i++) {
        if (result[i] == ' ') {
            wordCount++;
            if (wordCount == k) {
                result[i] = '\0';
                break;
            }
        }
    }
    
    return result;
}

int main() {
    char s[1000];
    fgets(s, sizeof(s), stdin);
    s[strcspn(s, "\n")] = 0;
    
    int k;
    scanf("%d", &k);
    
    char* result = solution(s, k);
    printf("%s\n", result);
    free(result);
    
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(n)

Split operation processes entire string, join processes k words

✓ Linear Growth

Space Complexity

O(n)

Array stores all words from the sentence

⚡ Linearithmic Space

25.0K Views

Medium Frequency

~8 min Avg. Time

890 Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Split and Join Approach — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler