3403. Find the Lexicographically Largest String From the Box I
Approach
Find lex-largest substring of length max(1, n - numFriends + 1) by direct scan.
Key Techniques
Array problems involve manipulating elements stored in a contiguous block of memory. Key techniques include two-pointer traversal, prefix sums, sliding windows, and in-place partitioning. In C#, arrays are zero-indexed and fixed in size — use List<T> when you need dynamic resizing.
String problems range from simple character counting to complex pattern matching. Common approaches include two pointers, sliding window, prefix hashing, and the KMP algorithm. In C#, strings are immutable — use StringBuilder for efficient concatenation inside loops.
Simulation problems require implementing the described process step by step. Focus on correctly handling edge cases and state transitions. Common in geometry, game problems, and string manipulation. Optimize only if the naive simulation exceeds the time limit.
// Approach: Find lex-largest substring of length max(1, n - numFriends + 1) by direct scan.
// Time: O(n²) Space: O(1)
public class Solution
{
public string AnswerString(string word, int numFriends)
{
// If there is only one friend, return the whole word as is.
if (numFriends == 1)
return word;
int wordLength = word.Length;
string answer = "";
// Iterate over each character of the word.
for (int i = 0; i < wordLength; ++i)
{
// Determine the maximum substring length that can be taken starting from the current position.
int maxSubstringLength = Math.Min(wordLength - i, wordLength - numFriends + 1);
// Extract the substring starting at position i with the determined length.
string currentSubstring = word.Substring(i, maxSubstringLength);
// Compare the current substring with the answer found so far and update if it is greater.
if (string.Compare(answer, currentSubstring) < 0)
answer = currentSubstring;
}
// Return the largest lexicographical substring found.
return answer;
}
}