What is the time complexity of Print Words Vertically?

The optimal solution has a time complexity of O(N*M).

What is the space complexity of Print Words Vertically?

The space complexity is O(N*M).

What data structures are used to solve Print Words Vertically?

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

What are the key insights for solving Print Words Vertically?

Insight 1: The core idea is to transpose the characters of the words. Each row in the input becomes a column in the output, and vice versa. Insight 2: The length of the longest word determines the number of rows in the output. This defines the iterations needed.

Which companies ask LeetCode 1324. Print Words Vertically in interviews?

This problem is frequently asked at Guidewire.

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Print Words Vertically - LeetCode 1324 Solution

Print Words Vertically - Complete Solution Guide

Print Words Vertically is LeetCode problem 1324, a Medium level challenge. This complete guide provides step-by-step explanations, multiple solution approaches, and optimized code in python3, java, cpp, c.

Problem Statement

Given a string s . Return all the words vertically in the same order in which they appear in s . Words are returned as a list of strings, complete with spaces when is necessary. (Trailing spaces are not allowed). Each word would be put on only one column and that in one column there will be only one word. Example 1: Input: s = "HOW ARE YOU" Output: ["HAY","ORO","WEU"] Explanation: Each word is printed vertically. "HAY" "ORO" "WEU" Example 2: Input: s = "TO BE OR NOT TO BE" Output: ["TBONTB","OER

Detailed Explanation

The problem asks us to take a string `s` consisting of multiple words separated by single spaces, and print the words vertically. This means constructing a list of strings where each string represents a column formed by characters from the input words. If a word is shorter than the maximum length among all words, we pad the corresponding position in the resulting string with a space. Trailing spaces in the output strings should be removed.

Solution Approach

The solution involves splitting the input string into individual words, finding the maximum length among these words, and then iterating to build the vertical strings. For each vertical string, we iterate through the words. If the current index is within the bounds of a word, we append the character at that index; otherwise, we append a space. Finally, we remove any trailing spaces from each constructed vertical string.

Step-by-Step Algorithm

Step 1: Split the input string `s` into a list of words using spaces as delimiters.
Step 2: Determine the maximum length (`maxLen`) among all the words in the list.
Step 3: Initialize an empty list `result` to store the vertically printed words.
Step 4: Iterate from `i = 0` to `maxLen - 1` (inclusive), representing the rows (vertical strings).
Step 5: Inside the outer loop, create a string builder `sb` to construct the i-th vertical string.
Step 6: Iterate through each word in the list of words.
Step 7: If the current row index `i` is within the length of the current word, append the character at index `i` to `sb`. Otherwise, append a space ' ' to `sb`.
Step 8: After iterating through all words, remove any trailing spaces from the string builder `sb`. This is done by iterating backward from the end of the string and truncating it until a non-space character is encountered.
Step 9: Convert the resulting string from the string builder `sb` to a string and add it to the `result` list.
Step 10: Return the `result` list containing the vertically printed words.

Key Insights

Insight 1: The core idea is to transpose the characters of the words. Each row in the input becomes a column in the output, and vice versa.
Insight 2: The length of the longest word determines the number of rows in the output. This defines the iterations needed.
Insight 3: Trailing spaces need to be removed from each output string to meet the problem requirements. This can be done efficiently using string manipulation techniques.

Complexity Analysis

Time Complexity: O(N*M)

Space Complexity: O(N*M)

Topics

This problem involves: Array, String, Simulation.

Companies

Asked at: Guidewire.

Print Words Vertically | LeetCode 1324

Medium

Array String Simulation

Time: O(N*M)Space: O(N*M)

Solution Code

Available in:

import java.util.ArrayList;
import java.util.List;

class Solution {
    public List<String> printVertically(String s) {
        String[] words = s.split(" ");
        int maxLen = 0;
        for (String word : words) {
            maxLen = Math.max(maxLen, word.length());
        }

        List<String> result = new ArrayList<>();
        for (int i = 0; i < maxLen; i++) {
            StringBuilder sb = new StringBuilder();
            for (String word : words) {
                if (i < word.length()) {
                    sb.append(word.charAt(i));
                } else {
                    sb.append(" ");
                }
            }
            
            int j = sb.length() - 1;
            while (j >= 0 && sb.charAt(j) == ' ') {
                j--;
            }
            
            result.add(sb.substring(0, j + 1).toString());
        }
        
        return result;
    }
}

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Problem Info

Description

Problem 1324: Print Words Vertically - Detailed explanation and solution approaches.

Topics

Array String Simulation

Companies

Guidewire

Stats

Difficulty:Medium

Languages:4

Companies:1

Problem #:1324

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

10 steps

1
Step 1: Split the input string `s` into a list of words using spaces as delimiters.
2
Step 2: Determine the maximum length (`maxLen`) among all the words in the list.
3
Step 3: Initialize an empty list `result` to store the vertically printed words.
4
Step 4: Iterate from `i = 0` to `maxLen - 1` (inclusive), representing the rows (vertical strings).
5
Step 5: Inside the outer loop, create a string builder `sb` to construct the i-th vertical string.
6
Step 6: Iterate through each word in the list of words.
7
Step 7: If the current row index `i` is within the length of the current word, append the character at index `i` to `sb`. Otherwise, append a space ' ' to `sb`.
8
Step 8: After iterating through all words, remove any trailing spaces from the string builder `sb`. This is done by iterating backward from the end of the string and truncating it until a non-space character is encountered.
9
Step 9: Convert the resulting string from the string builder `sb` to a string and add it to the `result` list.
10
Step 10: Return the `result` list containing the vertically printed words.

💡

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*M)

📝

Why?

The time complexity is derived from the nested loops: the outer loop iterates up to the maximum word length (M), and the inner loop iterates through all the words (N). The space complexity comes from storing the words after splitting, and the result, where each of M strings of length up to N can be stored. Therefore, it makes the space complexity O(N*M).

📖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 NumPy for Transposition (Python)

In Python, you could use NumPy to create a 2D character array from the words (padding with spaces as necessary) and then transpose the array to get the vertical arrangement. This can simplify the code.

Time: O(N*M)Space: O(N*M)

Trade-offs: Using NumPy introduces an external dependency, which might not be desirable in all situations. However, it can make the code more concise and potentially faster for large inputs due to optimized NumPy operations. This approach would involve padding each string to the max length before creating the numpy array.

✨

Key Insights

1Insight 1: The core idea is to transpose the characters of the words. Each row in the input becomes a column in the output, and vice versa.
2Insight 2: The length of the longest word determines the number of rows in the output. This defines the iterations needed.
3Insight 3: Trailing spaces need to be removed from each output string to meet the problem requirements. This can be done efficiently using string manipulation techniques.

📚

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 string. The code correctly handles this by returning an empty list, since the string will split into an empty array of words.
Edge case 2: Input string with only one word. The code will correctly print the word vertically as a list of single-character strings.
Edge case 3: Input string with words of varying lengths. The padding with spaces and removal of trailing spaces ensures correct output.

⚠️

Common Mistakes to Avoid

✗Common mistake 1: Forgetting to remove trailing spaces. This violates the problem constraints and leads to incorrect outputs.

✗Common mistake 2: Not handling words of different lengths properly, leading to incorrect character placement in the vertical strings.

✗Common mistake 3: Incorrectly calculating the maximum word length, leading to missing characters or incorrect padding.

✅

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: This type of transposition is analogous to data transformations done in database operations (pivoting or unpivoting data).

🏦Real-world scenario 2: This could be used in text processing and formatting applications to create stylized text displays or visual representations of data.

💡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

If stuck, try working through a small example by hand. The pattern often reveals itself.

⚠️ 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 4, 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

In a real interview, always clarify constraints first. Ask about input size and value ranges.

@TechLeadJul 13

Don't forget to handle the edge case when the input is empty. Many candidates miss this in interviews.

@DevExpert92Jul 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.

What techniques are commonly tested in medium-difficulty problems?

Medium problems often require combining multiple techniques: two-pointer with hash maps, BFS/DFS with state tracking, dynamic programming with optimization, or divide-and-conquer approaches. They test your ability to recognize patterns and choose the right combination of techniques.

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 "Print Words Vertically"?

For this medium-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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