Find the Lexicographically Largest String From the Box I - Problem

Alice is organizing an exciting word-splitting game for her friends! ๐ŸŽฎ

Given a string word and an integer numFriends, Alice runs multiple rounds where each round:

  • The word is split into exactly numFriends non-empty substrings
  • Each split must be unique - no two rounds can have the same split pattern
  • All resulting substrings are collected in a box

Your task is to find the lexicographically largest string that will be in the box after all possible unique splits are completed.

Example: If word = "abc" and numFriends = 2:

  • Split 1: ["a", "bc"] โ†’ box contains: "a", "bc"
  • Split 2: ["ab", "c"] โ†’ box contains: "a", "bc", "ab", "c"
  • Lexicographically largest: "c"

Input & Output

example_1.py โ€” Basic Split
$ Input: word = "abc", numFriends = 2
โ€บ Output: "c"
๐Ÿ’ก Note: Possible splits: ["a", "bc"], ["ab", "c"]. All substrings: "a", "ab", "bc", "c". Lexicographically largest is "c".
example_2.py โ€” Single Friend
$ Input: word = "leetcode", numFriends = 1
โ€บ Output: "leetcode"
๐Ÿ’ก Note: Only one split possible: ["leetcode"]. The entire word is the only and largest substring.
example_3.py โ€” Multiple Max Characters
$ Input: word = "aaaa", numFriends = 3
โ€บ Output: "aa"
๐Ÿ’ก Note: Possible splits include ["a", "a", "aa"], ["a", "aa", "a"], ["aa", "a", "a"]. The largest substring is "aa".

Visualization

Tap to expand
๐Ÿ• Pizza Cutting AnalogyabcbaCut into 3 piecesCutting Analysis:๐ŸŽฏ Target: 3 pieces (numFriends = 3)๐Ÿ• Premium ingredient: 'c' (largest char)โœ… Best piece: "cb" or "c" depending on cutsOptimal Strategy:1. Find all 'c' positions2. Try different piece sizes from 'c'3. Verify remaining can be cut properlyExample Cuts:"a""bc""ba"Cut 1"ab""c""ba"Cut 2๐Ÿ† Winner: "c"Lexicographically largest piece
Understanding the Visualization
1
Identify Premium Spots
Look for the largest character in the pizza - these are potential starting points for premium pieces
2
Test Cut Patterns
For each premium spot, try different piece sizes and check if valid cutting patterns exist
3
Validate Cuts
Ensure that after taking a piece, the remaining pizza can still be cut into the required number of pieces
4
Select Best Piece
Among all valid pieces, choose the lexicographically largest one
Key Takeaway
๐ŸŽฏ Key Insight: Instead of generating all possible cuts (expensive), focus on positions with the largest character and verify if valid cutting patterns exist. This reduces complexity from exponential to polynomial time.

Time & Space Complexity

Time Complexity
โฑ๏ธ
O(C(n-1, k-1) * n)

C(n-1, k-1) ways to choose split positions, each requiring O(n) time to generate substrings

n
2n
โœ“ Linear Growth
Space Complexity
O(n * C(n-1, k-1))

Storing all possible substrings from all splits

n
2n
โšก Linearithmic Space

Constraints

  • 1 โ‰ค numFriends โ‰ค word.length โ‰ค 1000
  • word consists of lowercase English letters
  • Each split must produce exactly numFriends non-empty substrings
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