LeetCode Solutions in Java

A structured collection of LeetCode solutions written in Java. Every solution includes a clear explanation of the approach and complexity analysis — because understanding the why matters more than just passing the test.

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What You'll Find Here

• Clean, well-commented Java code
• Approach explained in plain English for every problem
• Time and Space complexity on every solution
• Organized by topic — not just dumped in one folder

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Topics

Topic	Key Patterns
Arrays	Two pointers, sliding window, prefix sum
Strings	HashMap, sliding window, palindrome
Trees	DFS, BFS, recursion, level order
Graphs	DFS, BFS, topological sort, union find
Dynamic Programming	Memoization, tabulation, state design
Sorting	Merge sort, quick select, counting sort
Linked Lists	Fast/slow pointers, reversal, merge
Stack & Queue	Monotonic stack, deque, min stack
Binary Search	Search space reduction, rotated arrays
Math	Number theory, bit manipulation, GCD

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Solution Format

Every file follows this structure:

// Problem: Two Sum (Easy) — LeetCode #1
// Link: https://leetcode.com/problems/two-sum/
// Approach: Store each number's complement in a HashMap.
//           On each iteration, check if the complement already exists.
// Time Complexity: O(n)
// Space Complexity: O(n)

class Solution {
    public int[] twoSum(int[] nums, int target) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            if (map.containsKey(complement))
                return new int[]{map.get(complement), i};
            map.put(nums[i], i);
        }
        return new int[]{};
    }
}

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How I Approach Problems

1. READ     ->  Understand fully before touching the keyboard
2. BRUTE    ->  Naive solution first — get it working
3. PATTERN  ->  Sliding window? DP? Graph traversal? Find it.
4. OPTIMIZE ->  Reduce time and space, justify every step
5. CODE     ->  Clean implementation with meaningful names
6. PUSH     ->  Daily commit. Consistency over everything.

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Connect

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