How do you solve Find the String with LCP on LeetCode?

Find the String with LCP (LeetCode #2573) can be solved using Brute Force or Optimal Solution. The optimal approach is Optimal Solution with O(n) time complexity and O(n) space complexity. Key insight: Understanding the LCP matrix is crucial for constructing the string correctly.

What is the brute force solution for Find the String with LCP?

The brute force approach for Find the String with LCP is Brute Force, with O(n²) time complexity and O(1) space complexity. We can generate all possible strings from the LCP matrix and check which one matches the conditions. This is straightforward but inefficient. The optimal Optimal Solution approach improves this to O(n).

What algorithm or data structure is used to solve Find the String with LCP?

Find the String with LCP uses the following concepts: Array, String, Dynamic Programming, Greedy, Union-Find, Matrix. The recommended patterns to study are: Dynamic Programming, Greedy Algorithms.

What are the interview tips for Find the String with LCP?

Always explain your thought process while coding. Consider edge cases and test your solution against them. Ask clarifying questions about the problem to ensure you understand the requirements.

What are common mistakes when solving Find the String with LCP?

Failing to validate the constructed string against the LCP matrix. Not considering edge cases where the LCP values might contradict.

#2573

Find the String with LCP

Hard

ArrayStringDynamic ProgrammingGreedyUnion-FindMatrixDynamic ProgrammingGreedy Algorithms

LeetCode ↗

Approaches

Brute ForceOptimal

Complexity Comparison

	Brute Force	Optimal Solution★
Time	O(n²)	O(n)
Space	O(1)	O(n)

💡

Intuition

Time O(n)Space O(n)

We can leverage the LCP matrix to directly construct the string by determining character groups based on the LCP values, ensuring we maintain lexicographical order.

⚙️

Algorithm

5 steps

1Step 1: Initialize a character array of size n to store the result.
2Step 2: Assign characters based on the longest common prefix lengths, ensuring that the same characters are assigned to indices that require them to be equal.
3Step 3: Use a greedy approach to assign the smallest available character to each group of equal indices.
4Step 4: Validate the constructed string against the LCP matrix.
5Step 5: Return the constructed string or an empty string if validation fails.

solution.py28 lines

1# Full working Python code
2class Solution:
3    def findTheString(self, lcp):
4        n = len(lcp)
5        word = [''] * n
6        for i in range(n):
7            if word[i] == '':
8                word[i] = 'a'
9            for j in range(i + 1, n):
10                if lcp[i][j] > 0:
11                    word[j] = word[i]
12                elif lcp[i][j] == 0:
13                    word[j] = chr(ord(word[i]) + 1)
14        return ''.join(word) if self.isValid(word, lcp) else ''
15
16    def isValid(self, word, lcp):
17        n = len(word)
18        for i in range(n):
19            for j in range(n):
20                if self.lcp(word, i, j) != lcp[i][j]:
21                    return False
22        return True
23
24    def lcp(self, word, i, j):
25        count = 0
26        while i + count < len(word) and j + count < len(word) and word[i + count] == word[j + count]:
27            count += 1
28        return count

ℹ

Complexity note: The time complexity is O(n) because we iterate through the LCP matrix only once to construct the string. The space complexity is O(n) due to the storage of the result string.

1Understanding the LCP matrix is crucial for constructing the string correctly.
2Character assignments must respect the constraints imposed by the LCP values.

Solutions and explanations are original Tejav content. Problem titles © LeetCode — use the LeetCode button above for the full problem statement.