You are given a string word
, and an integer numFriends
.
Alice is organizing a game for her numFriends
friends. There are multiple rounds in the game, where in each round:
word
is split into numFriends
non-empty strings, such that no previous round has had the exact same split.Find the lexicographically largest string from the box after all the rounds are finished.
Example 1:
Input: word = "dbca", numFriends = 2
Output: "dbc"
Explanation:
All possible splits are:
"d"
and "bca"
."db"
and "ca"
."dbc"
and "a"
.Example 2:
Input: word = "gggg", numFriends = 4
Output: "g"
Explanation:
The only possible split is: "g"
, "g"
, "g"
, and "g"
.
Constraints:
1 <= word.length <= 5 * 10^3
word
consists only of lowercase English letters.1 <= numFriends <= word.length
When you get asked this question in a real-life environment, it will often be ambiguous (especially at FAANG). Make sure to ask these questions in that case:
The brute force approach for this problem involves trying out every possible combination of characters we can pick from the input box. We will then compare these combinations to see which one is the 'biggest' alphabetically, according to the rules of lexicographical ordering.
Here's how the algorithm would work step-by-step:
def find_lexicographically_largest_string_brute_force(input_string):
all_possible_strings = []
def generate_strings(current_string, remaining_characters):
all_possible_strings.append(current_string)
# If no characters remain, then we can't make additional combinations.
if not remaining_characters:
return
for index in range(len(remaining_characters)):
# Build all combinations by choosing a starting character
generate_strings(
current_string + remaining_characters[index],
remaining_characters[index+1:]
)
generate_strings("", input_string)
# Find the lexicographically largest string in the list
lexicographically_largest_string = ""
for possible_string in all_possible_strings:
# Compare and update if larger than current largest string
if possible_string > lexicographically_largest_string:
lexicographically_largest_string = possible_string
return lexicographically_largest_string
The main idea is to build the lexicographically largest string one character at a time by always choosing the largest available character. We repeatedly select the largest character that can be legally added to the current string without violating the constraints of the box.
Here's how the algorithm would work step-by-step:
def find_lexicographically_largest_string(character_counts):
string_length = sum(character_counts.values())
result = ""
character_counts_copy = character_counts.copy()
for _ in range(string_length):
for char_code in range(ord('z'), ord('a') - 1, -1):
current_character = chr(char_code)
# Check if the character is available.
if character_counts_copy.get(current_character, 0) > 0:
character_counts_copy[current_character] -= 1
remaining_length = string_length - len(result) - 1
remaining_counts = sum(character_counts_copy.values())
# Check if we can still complete the string.
if remaining_counts >= remaining_length:
result += current_character
break
else:
# If we can't complete the string, backtrack.
character_counts_copy[current_character] += 1
return result
Case | How to Handle |
---|---|
Null or empty input string | Return an empty string or throw an IllegalArgumentException if the input is null or empty. |
All characters in the input string are the same | The solution should still return a lexicographically largest permutation, even if all characters are identical. |
Input string already sorted in descending order | The algorithm should still correctly identify this as the lexicographically largest string and return it. |
Input string with very long length causing potential memory issues | The implementation should use efficient data structures and algorithms to minimize memory usage and prevent out-of-memory errors if the string is extremely long. |
Input String consists of unicode/non-ascii characters | Ensure the string comparison and sorting algorithm supports unicode characters correctly. |
Box contains insufficient characters to generate even a single valid string | Return an empty string or null to signify there is no possible string. |
The 'greedy' character selection might prematurely terminate the algorithm before a better choice is found | Backtracking or dynamic programming might be necessary to ensure the globally optimal largest string is generated. |
Integer overflow if using counters to track character counts in very large strings | Use appropriate data types (e.g., long) or handle potential overflow scenarios to ensure accurate character counting. |