LeetCode 2573 | Find the String with LCP | Java | Hard | Greedy & Dynamic Programming | CodeByTushu
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In today’s video, we solve LeetCode 2573 — Find the String with LCP using Greedy and Dynamic Programming in Java.
We are given an n by n matrix representing the Longest Common Prefix (LCP) between all pairs of suffixes of an unknown string. Our task is to reconstruct the lexicographically smallest lowercase English string that generates this exact matrix, or return an empty string if no such string can exist.
We apply a two-stage approach: first, we greedily assign the smallest available English letters ('a' through 'z') to unvisited indices, grouping matching positions where lcp[i][j] is greater than zero. Second, since arbitrary inputs may contain transitivity violations, asymmetric relations, or impossible length values, we validate our candidate string using bottom-up dynamic programming in optimal O(n^2) time and O(n) auxiliary space.
🔥 Problem Highlights
✅ Greedy left-to-right character assignment ensuring lexicographical minimality
✅ Character grouping based on positive longest common prefix values
✅ Immediate early termination if more than 26 distinct character classes are needed
✅ Robust verification using bottom-up 2D Dynamic Programming
✅ Guarding against self-contradictions, invalid diagonals, and asymmetry
✅ Optimal O(n^2) time complexity and O(n) auxiliary space
⏱️ TIMESTAMPS
00:00 Intro & Daily Challenge Overview
01:25 Problem Understanding & LCP Matrix Definition
03:30 Key Observations: Greedy Lexicographical Assignment & 26-Character Limit
05:44 Algorithmic Strategy: Backward 2D DP Verification
07:27 Clean Java Solution Walkthrough Line by Line
09:02 Dry Run & Step-by-Step Example Walkthrough
12:00 Time Complexity Analysis (O(N^2) - 10 ms, Beats 98.6%)
13:10 Space Complexity Analysis (O(N) Auxiliary Space)
14:00 Outro & Resources
📂 Problem Folder & Detailed Documentation:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/tree/main/solutions/March/28-March/2573-Find-the-String-with-LCP
☕ Java Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/Solution.java
🐍 Python Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.py
⚡ C++ Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.cpp
🌐 JavaScript Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.js
🔗 LeetCode Source Code
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🔥 Perfect For
LeetCode Hard Problems
Java DSA Preparation
String Reconstruction Patterns
Longest Common Prefix (LCP)
Dynamic Programming DP Verification
Greedy Strategy Algorithms
Coding Interview Preparation
Problem Solving
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💬 Question of the Day
Why is it essential to re-verify the candidate string with a 2D DP check after greedy construction?
1️⃣ Because the input LCP matrix may contain invalid values, transitivity conflicts, or impossible suffix lengths that cannot correspond to any real string
2️⃣ Because lowercase letters only allow strings of length at most 26
3️⃣ Because the greedy step only checks odd indices
4️⃣ Because dynamic programming is required to find the string's length
#LeetCode2573 #LeetCode #FindTheStringWithLCP #Java #JavaDSA #String #DynamicProgramming #Greedy #Matrix #DSA #CodingInterview #ProblemSolving #LeetCodeHard #DailyLeetCode #JavaProgramming #CodeByTushu
👇 Comment the answer below! 🔥 Close description
In today’s video, we solve LeetCode 2573 — Find the String with LCP using Greedy and Dynamic Programming in Java.
We are given an n by n matrix representing the Longest Common Prefix (LCP) between all pairs of suffixes of an unknown string. Our task is to reconstruct the lexicographically smallest lowercase English string that generates this exact matrix, or return an empty string if no such string can exist.
We apply a two-stage approach: first, we greedily assign the smallest available English letters ('a' through 'z') to unvisited indices, grouping matching positions where lcp[i][j] is greater than zero. Second, since arbitrary inputs may contain transitivity violations, asymmetric relations, or impossible length values, we validate our candidate string using bottom-up dynamic programming in optimal O(n^2) time and O(n) auxiliary space.
🔥 Problem Highlights
✅ Greedy left-to-right character assignment ensuring lexicographical minimality
✅ Character grouping based on positive longest common prefix values
✅ Immediate early termination if more than 26 distinct character classes are needed
✅ Robust verification using bottom-up 2D Dynamic Programming
✅ Guarding against self-contradictions, invalid diagonals, and asymmetry
✅ Optimal O(n^2) time complexity and O(n) auxiliary space
⏱️ TIMESTAMPS
00:00 Intro & Daily Challenge Overview
01:25 Problem Understanding & LCP Matrix Definition
03:30 Key Observations: Greedy Lexicographical Assignment & 26-Character Limit
05:44 Algorithmic Strategy: Backward 2D DP Verification
07:27 Clean Java Solution Walkthrough Line by Line
09:02 Dry Run & Step-by-Step Example Walkthrough
12:00 Time Complexity Analysis (O(N^2) - 10 ms, Beats 98.6%)
13:10 Space Complexity Analysis (O(N) Auxiliary Space)
14:00 Outro & Resources
📂 Problem Folder & Detailed Documentation:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/tree/main/solutions/March/28-March/2573-Find-the-String-with-LCP
☕ Java Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/Solution.java
🐍 Python Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.py
⚡ C++ Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.cpp
🌐 JavaScript Solution:
https://github.com/CodeByTushu/CodeByTushu-LeetCode-Solutions/blob/main/solutions/March/28-March/2573-Find-the-String-with-LCP/solution.js
🔗 LeetCode Source Code
📌 Admin type the link
🌐 All LeetCode Solutions
📌 https://codebytushu.com/Leetcode/
📱 Join CodeByTushu on WhatsApp
Get coding updates, LeetCode solutions, daily questions and more.
https://whatsapp.com/channel/0029Vb8k5mCDeON2Xwlkxe40
❤️ Donate
📌 https://codebytushu.com/Leetcode/donate.php
🔥 Perfect For
LeetCode Hard Problems
Java DSA Preparation
String Reconstruction Patterns
Longest Common Prefix (LCP)
Dynamic Programming DP Verification
Greedy Strategy Algorithms
Coding Interview Preparation
Problem Solving
🌐 Follow CodeByTushu
▶️ YouTube: https://www.youtube.com/@codebytushu
📸 Instagram: https://instagram.com/codebytushu/
💼 LinkedIn: https://www.linkedin.com/company/codebytushu/
🌍 Website: https://codebytushu.com
🐙 GitHub: https://github.com/CodeByTushu
❤️ Don’t Forget To
👍 Like | 💬 Comment | 🔔 Subscribe
💬 Question of the Day
Why is it essential to re-verify the candidate string with a 2D DP check after greedy construction?
1️⃣ Because the input LCP matrix may contain invalid values, transitivity conflicts, or impossible suffix lengths that cannot correspond to any real string
2️⃣ Because lowercase letters only allow strings of length at most 26
3️⃣ Because the greedy step only checks odd indices
4️⃣ Because dynamic programming is required to find the string's length
#LeetCode2573 #LeetCode #FindTheStringWithLCP #Java #JavaDSA #String #DynamicProgramming #Greedy #Matrix #DSA #CodingInterview #ProblemSolving #LeetCodeHard #DailyLeetCode #JavaProgramming #CodeByTushu
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