Mastering Sliding Window for Efficient Substring Counting

🚀 Day 90 – DSA Journey | Binary Tree Paths Continuing my daily DSA practice, today I explored how to track and construct paths in a binary tree. 📌 Problem Practiced: Binary Tree Paths (LeetCode 257) 🔍 Problem Idea: Return all root-to-leaf paths in a binary tree as strings. 💡 Key Insight: While traversing the tree, we can build the path step by step. Once we reach a leaf node, we add the complete path to the result. 📌 Approach Used: • Use DFS traversal • Maintain a string to track the current path • At each node, append its value to the path • If it’s a leaf node → add the path to result • Continue exploring left and right subtrees 📌 Concepts Strengthened: • Tree traversal (DFS) • Recursion • Path tracking • String manipulation ⏱️ Time Complexity: O(n) 📦 Space Complexity: O(h) (recursion stack) 🔥 Today’s takeaway: Tracking state (like a path) during recursion is a powerful technique for solving tree problems. On to Day 91! 🚀 #Day90 #DSAJourney #LeetCode #BinaryTree #DFS #Java #ProblemSolving #Coding #LearningInPublic #Consistency

🚀 Day 84 – DSA Journey | Maximum Depth of Binary Tree Continuing my daily DSA practice, today I focused on understanding tree depth and recursive problem solving. 📌 Problem Practiced: Maximum Depth of Binary Tree (LeetCode 104) 🔍 Problem Idea: Find the maximum depth (or height) of a binary tree — the number of nodes along the longest path from the root to a leaf node. 💡 Key Insight: The depth of a tree depends on its subtrees. At every node, we can recursively calculate the depth of left and right subtrees and take the maximum. 📌 Approach Used: • If the node is null → depth is 0 • Recursively calculate depth of left subtree • Recursively calculate depth of right subtree • Return 1 + max(left, right) 📌 Concepts Strengthened: • Binary tree traversal • Recursion • Divide and conquer approach • Tree height calculation ⏱️ Time Complexity: O(n) 📦 Space Complexity: O(h) (recursion stack) 🔥 Today’s takeaway: Breaking problems into smaller subproblems using recursion makes complex tree problems much easier to handle. On to Day 85! 🚀 #Day84 #DSAJourney #LeetCode #BinaryTree #Recursion #Java #ProblemSolving #Coding #LearningInPublic #Consistency

🚀 Day 82 – DSA Journey | Same Tree using Recursion Continuing my daily DSA practice, today I worked on a problem that strengthened my understanding of tree comparison and recursion. 📌 Problem Practiced: Same Tree (LeetCode 100) 🔍 Problem Idea: Given two binary trees, determine whether they are identical in both structure and node values. 💡 Key Insight: To check if two trees are the same, we need to compare nodes at every level — both their values and their left & right subtrees. Recursion makes this process clean and intuitive. 📌 Approach Used: • If both nodes are null → trees match at this point • If one is null or values differ → trees are not the same • Recursively compare left subtrees • Recursively compare right subtrees • Both sides must match for the trees to be identical 📌 Concepts Strengthened: • Tree traversal • Recursion • Structural comparison • Base case handling ⏱️ Time Complexity: O(n) 📦 Space Complexity: O(h) (recursion stack) 🔥 Today’s takeaway: Tree problems often become simple when broken down recursively — solve smaller subtrees to solve the whole tree. On to Day 83! 🚀 #Day82 #DSAJourney #LeetCode #BinaryTree #Recursion #Java #ProblemSolving #Coding #LearningInPublic #Consistency

🚀 Day 86 – DSA Journey | Path Sum in Binary Tree Continuing my daily DSA practice, today I worked on a problem that strengthened my understanding of recursion and root-to-leaf traversal. 📌 Problem Practiced: Path Sum (LeetCode 112) 🔍 Problem Idea: Determine if there exists a root-to-leaf path in a binary tree such that the sum of node values equals a given target. 💡 Key Insight: Instead of tracking the full path, we can reduce the problem by subtracting the current node’s value from the target as we traverse down the tree. 📌 Approach Used: • If the node is null → return false • Check if it is a leaf node – If yes, compare node value with remaining target • Subtract current node value from target • Recursively check left and right subtrees • If any path matches → return true 📌 Concepts Strengthened: • Tree traversal • Recursion • Root-to-leaf path logic • Problem reduction technique ⏱️ Time Complexity: O(n) 📦 Space Complexity: O(h) (recursion stack) 🔥 Today’s takeaway: Breaking down a problem step by step (reducing the target at each node) makes recursion much more intuitive. On to Day 87! 🚀 #Day86 #DSAJourney #LeetCode #BinaryTree #Recursion #Java #ProblemSolving #Coding #LearningInPublic #Consistency

🚀 LeetCode Challenge 7/50 🔍 Problem: Valid Anagram Today’s problem was about checking whether two strings are anagrams of each other efficiently. 💡 Approach: I used the Character Frequency Count method: First checked if both strings have equal length Used an array of size 26 to track character frequencies Incremented counts for one string and decremented for the other If all values are zero, both strings are anagrams ⚡ This approach avoids sorting and ensures optimal performance. 📊 Complexity Analysis: Time Complexity: O(n) Space Complexity: O(1) 📚 Key Learning: Using frequency arrays is a powerful technique for string problems. It helps achieve constant space complexity and improves efficiency compared to sorting-based approaches. Step by step, getting better at problem solving 💪 #LeetCode #Algorithms #DataStructures #ProblemSolving #CodingJourney #Java #100DaysOfCode #StudentDeveloper #Learning

🚀 Day 54 of My LeetCode Journey 🔍 Problem: Find the Index of the First Occurrence in a String Today’s problem focused on searching for a substring inside a string — a very common concept in interviews and real-world applications like text processing and search engines. 💡 Key Idea: We compare the substring (needle) with every possible starting position in the main string (haystack) until we find a match. 🧠 What I Learned: How string matching works internally Importance of boundary conditions (like empty strings) Difference between brute-force and optimized approaches Why built-in methods like indexOf() are efficient ⚡ Approaches: Using built-in method (indexOf) – simple and efficient Manual iteration (brute force) – helps understand logic deeply 📈 Time Complexity: O(n * m) for brute-force approach 🔥 Takeaway: Even simple problems can teach core fundamentals. Mastering these basics builds a strong foundation for advanced algorithms like KMP. #Day54 #LeetCode #Java #DataStructures #CodingJourney #Programming #InterviewPreparation

#Day75 of my second #100DaysOfCode Today’s problem was more about spotting patterns than writing code. DSA • Solved Single Element in a Sorted Array (LeetCode 540, Medium) – Brute: linear scan checking pairs → O(n) – Optimal: binary search using index pattern → O(log n) • Key idea: elements appear in pairs, and the single element breaks this pattern • Used position-based logic to decide which half to search This one really showed how observing patterns can simplify the approach. #DSA #BinarySearch #LeetCode #Algorithms #Java #100DaysOfCode #WomenWhoCode #BuildInPublic #LearningInPublic

Day 09 of #50DaysOfLeetCode Challenge Just tackled the "Combination Sum" problem! This was a fantastic exercise in backtracking. The challenge is to find all unique combinations of numbers that sum up to a specific target, with the twist that you can use the same number multiple times. Key Insights: Backtracking Power: It’s all about exploring every possible path and "backtracking" as soon as the sum exceeds the target. State Space Tree: Visualizing how the recursion branches out helped me understand how to avoid duplicate combinations while allowing multiple uses of the same element. Decision Making: Learning when to include an element and when to move to the next index is crucial for optimizing the search. Each day, the logic gets sharper and the problems get more interesting! #DataStructures #Algorithms #CodingJourney #Java #Backtracking #LeetCode #ProblemSolving #SoftwareEngineering

🚀 Day 83 – DSA Journey | Symmetric Tree (Mirror Check) Continuing my daily DSA practice, today I worked on a problem that deepened my understanding of tree symmetry and recursion. 📌 Problem Practiced: Symmetric Tree (LeetCode 101) 🔍 Problem Idea: Check whether a binary tree is a mirror of itself — i.e., symmetric around its center. 💡 Key Insight: A tree is symmetric if the left subtree is a mirror reflection of the right subtree. This can be checked by comparing nodes in a cross manner. 📌 Approach Used: • Compare the tree with itself using a helper function • If both nodes are null → symmetric at this level • If one is null or values differ → not symmetric • Recursively compare: – Left of first subtree with right of second – Right of first subtree with left of second 📌 Concepts Strengthened: • Tree traversal • Recursion • Mirror / symmetry logic • Structural comparison ⏱️ Time Complexity: O(n) 📦 Space Complexity: O(h) (recursion stack) 🔥 Today’s takeaway: Many tree problems become easier when visualized as mirror or reflection comparisons. On to Day 84! 🚀 #Day83 #DSAJourney #LeetCode #BinaryTree #Recursion #Java #ProblemSolving #Coding #LearningInPublic #Consistency