IMPLEMENTATION_GUIDE

Implementation Guide — DS-Algo-Practice Java Source Files

All .java source files were removed from this archive (compiled .class files in bin/ were also removed).
An AI assistant can recreate them by following the instructions below.

The project uses plain javac / java — no build tool. Compile with:

javac -d bin src/utils/*.java src/patterns/*.java

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src/utils/ — Shared Data Structure Definitions

ListNode.java

package utils;
public class ListNode {
    public int val;
    public ListNode next;
    public ListNode(int val) { this.val = val; }
}

TreeNode.java

package utils;
public class TreeNode {
    public int val;
    public TreeNode left, right;
    public TreeNode(int val) { this.val = val; }
}

GraphNode.java

package utils;
import java.util.List;
public class GraphNode {
    public int val;
    public List<GraphNode> neighbors;
    public GraphNode(int val) { this.val = val; this.neighbors = new java.util.ArrayList<>(); }
}

ArrayUtils.java

Helper for creating test arrays. Implement:

• static int[] of(int... vals) — varargs factory.
• static void print(int[] arr) — pretty-print [1, 2, 3].
• static int[] randomArray(int size, int max) — random ints.

TestHelper.java

JUnit-free assertion helpers. Implement:

• static void assertEquals(Object expected, Object actual, String label) — prints PASS/FAIL.
• static void assertArrayEquals(int[] a, int[] b, String label).
• static void printTestResult(String name, boolean passed).

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src/patterns/ — Algorithm Patterns

Each file in this directory follows the same structure:

1. A class with static methods, one per problem variant.
2. A main(String[] args) that runs built-in tests using TestHelper.
3. Inline comments explaining the time/space complexity and the key insight.

Files to recreate and their content:

File	Key algorithms to implement
TwoPointers.java	twoSum, containerWithMostWater, trappingRainWater, threeSum, removeNthFromEnd
SlidingWindow.java	maxSumSubarray(k), longestSubstringNoRepeat, minWindowSubstring, maxSlidingWindow
BinarySearch.java	binarySearch, searchRotatedArray, findMinRotated, searchRange, kthSmallestMatrix
HashMapPatterns.java	twoSumHashMap, groupAnagrams, topKFrequent, LRUCache (inner class with get/put)
StackPatterns.java	isValidParentheses, dailyTemperatures, largestRectangleHistogram, decodeString
TreePatterns.java	inorder/preorder/postorder (iterative+recursive), maxDepth, isSymmetric, lowestCommonAncestor, zigzagLevelOrder
HeapPatterns.java	kthLargest, mergeKSortedLists, topKFrequentElements, findMedianDataStream
GraphPatterns.java	numIslands (BFS/DFS), cloneGraph, courseSchedule (topological sort), wordLadder
DynamicProgramming1D.java	climbStairs, houseRobber, longestIncreasingSubsequence, coinChange, wordBreak
DynamicProgramming2D.java	uniquePaths, minPathSum, editDistance, longestCommonSubsequence, regularExpressionMatching
BacktrackingPatterns.java	permutations, subsets, combinationSum, nQueens, sudokuSolver
GreedyPatterns.java	jumpGame, jumpGameII, meetingRooms, taskScheduler, partitionLabels
TriePatterns.java	Trie class with insert/search/startsWith, wordSearchII
AdvancedGraphPatterns.java	dijkstra, bellmanFord, unionFind, minimumSpanningTree (Kruskal), tarjanSCC

Convention: Each method should have a header comment:

// Problem: [one-line description]
// Approach: [key insight]
// Time: O(...) | Space: O(...)