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Keyboard Row

Difficulty: Easy

Problem Description

Given an array of strings words, return the words that can be typed using letters of the alphabet on only one row of American keyboard.

Key Insights

  • The American keyboard consists of three rows:
    • First row: "qwertyuiop"
    • Second row: "asdfghjkl"
    • Third row: "zxcvbnm"
  • The problem is case-insensitive, meaning 'A' and 'a' are treated the same.
  • We need to identify which row each word is composed of and return only those that can be typed using letters from one row.

Space and Time Complexity

Time Complexity: O(N * M), where N is the number of words and M is the maximum length of a word. Space Complexity: O(1) for the row sets, O(K) for the output where K is the number of valid words.

Solution

To solve the problem, we can use the following approach:

  1. Create a set for each row of the keyboard that contains all the letters of that row.
  2. For each word in the input array, convert it to lowercase and check which row it belongs to by checking the letters against the sets.
  3. If all letters of the word belong to the same row set, add it to the result list.
  4. Finally, return the list of words that can be typed using only one row.

Code Solutions

def findWords(words):
    # Define the sets for each row of the keyboard
    row1 = set("qwertyuiop")
    row2 = set("asdfghjkl")
    row3 = set("zxcvbnm")
    
    # List to hold the result
    result = []
    
    for word in words:
        # Convert word to lowercase
        lowercase_word = word.lower()
        
        # Determine which row the first letter belongs to
        if lowercase_word[0] in row1:
            current_row = row1
        elif lowercase_word[0] in row2:
            current_row = row2
        else:
            current_row = row3
        
        # Check if all characters belong to the same row
        if all(char in current_row for char in lowercase_word):
            result.append(word)
    
    return result
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