LeetCode Challenge Day 18: Count Submatrices with Top-Left Element and Sum ≤ k

🚀 Day 19 of 100 Days LeetCode Challenge Problem: Count Submatrices With Equal Frequency of X and Y Today’s problem was a solid combination of 2D Prefix Sum + Hashing concept 🔥 💡 Key Insight: We need submatrices that: Include the top-left cell (0,0) Have equal number of 'X' and 'Y' Contain at least one 'X' 👉 Trick: Convert the grid into values: 'X' → +1 'Y' → -1 '.' → 0 🔍 Core Approach: 1️⃣ 2D Prefix Sum Transformation Build prefix sum based on above conversion 2️⃣ Check Each Submatrix (0,0 → i,j) If sum == 0 → equal number of X and Y ✅ 3️⃣ Extra Condition: Ensure at least one 'X' exists 👉 Track X count separately using another prefix matrix 🔥 What I Learned Today: Transforming problems into numbers simplifies logic Prefix sums + condition checks = powerful combo Always handle extra constraints carefully 📈 Challenge Progress: Day 19/100 ✅ Almost hitting Day 20! LeetCode, Prefix Sum, Matrix, Hashing, Problem Transformation, Algorithms, DSA Practice, Coding Challenge, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #PrefixSum #Matrix #Hashing #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep

Day 72 on LeetCode Search a 2D Matrix 🔍📊✅ Today’s problem was a great application of Binary Search in 2D, breaking it down into two efficient steps. 🔹 Approach Used in My Solution The goal was to determine whether a target exists in a sorted 2D matrix. Key idea in the solution: • First, apply binary search on rows to find the potential row where the target could exist   – Check if target lies between matrix[mid][0] and matrix[mid][cols-1] • Once the correct row is found, apply binary search within that row • Return true if found, otherwise false This avoids scanning the entire matrix and ensures efficiency. 🔹 Why This Works Because: • Each row is sorted • The first element of each row is greater than the last of the previous row So we can treat it like a two-level binary search problem. ⚡ Complexity: • Time Complexity: O(log m + log n) • Space Complexity: O(1) 💡 Key Takeaways: • Learned how to extend binary search to 2D structures • Practiced breaking problems into smaller searchable spaces • Reinforced thinking in terms of hierarchical searching 🔥 Another solid step in mastering binary search patterns! #LeetCode #DSA #Algorithms #DataStructures #BinarySearch #Matrix #2DArray #ProblemSolving #Coding #Programming #Cpp #STL #SoftwareEngineering #ComputerScience #CodingPractice #DeveloperLife #TechJourney #CodingDaily #100DaysOfCode #BuildInPublic #AlgorithmPractice #CodingSkills #Developers #TechCommunity #SoftwareDeveloper #EngineeringJourney

Day 77 on LeetCode Find Smallest Letter Greater Than Target 🔤🔍✅ Continuing the streak with a clean Binary Search application — keeping things simple and consistent during mids 💯 🔹 Approach Used in My Solution The goal was to find the smallest character strictly greater than the target in a sorted array, with wrap-around behavior. Key idea: • Apply binary search on the sorted array • Whenever letters[mid] > target, store it as a potential answer • Move left to find an even smaller valid character • If no such character exists, return letters[0] (wrap-around case) This ensures we always get the next greatest letter efficiently. ⚡ Complexity: • Time Complexity: O(log n) • Space Complexity: O(1) 💡 Key Takeaways: • Practiced binary search for “next greater element” problems • Learned how to handle wrap-around edge cases • Reinforced writing clean and optimized search logic 🔥 Small wins every day consistency is the real progress. #LeetCode #DSA #Algorithms #DataStructures #BinarySearch #Arrays #ProblemSolving #Coding #Programming #Cpp #STL #SoftwareEngineering #ComputerScience #CodingPractice #DeveloperLife #TechJourney #CodingDaily #Consistency #100DaysOfCode #BuildInPublic #AlgorithmPractice #CodingSkills #Developers #TechCommunity #SoftwareDeveloper #EngineeringJourney

Day 79 on LeetCode Smallest Index With Digit Sum Equal to Index 🔢✅ Keeping the streak going with a simple yet interesting digit manipulation + simulation problem 💯 🔹 Approach Used in My Solution The goal was to find the smallest index i such that the sum of digits of nums[i] equals i. Key idea: • Traverse the array from left to right • For each element, calculate the digit sum • Compare it with the current index • Return the first index where the condition satisfies • If none found → return -1 A clean and direct implementation without overcomplication. ⚡ Complexity: • Time Complexity: O(n * d) (d = number of digits) • Space Complexity: O(1) 💡 Key Takeaways: • Practiced digit extraction using modulo and division • Reinforced writing simple simulation-based solutions • Reminder: not every problem needs optimization — clarity matters 🔥 Consistency maintained, step by step progress continues. #LeetCode #DSA #Algorithms #DataStructures #Arrays #Math #Simulation #ProblemSolving #Coding #Programming #Cpp #STL #SoftwareEngineering #ComputerScience #CodingPractice #DeveloperLife #TechJourney #CodingDaily #Consistency #100DaysOfCode #BuildInPublic #AlgorithmPractice #CodingSkills #Developers #TechCommunity #SoftwareDeveloper #EngineeringJourney

🚀 Day 24 of 100 Days LeetCode Challenge Problem: Construct Product Matrix Today’s problem is a 2D extension of a classic concept: 👉 “Product of Array Except Self” 🔥 💡 Key Insight: For each cell (i, j), we need: Product of all elements except grid[i][j] Without using division (important!) 🔍 Core Approach: 1️⃣ Flatten the Matrix Treat the matrix like a 1D array 2️⃣ Prefix Product Store product of elements before index 3️⃣ Suffix Product Store product of elements after index 4️⃣ Final Value: p[i][j] = prefix * suffix % 12345 👉 This avoids division and works efficiently 💡 Optimization: Use modulo at every step to prevent overflow Space can be optimized by reusing arrays 🔥 What I Learned Today: Classic problems can appear in different forms (1D → 2D) Prefix & suffix patterns are extremely reusable Avoiding division is a common constraint in interviews 📈 Challenge Progress: Day 24/100 ✅ Almost 25 days strong! LeetCode, Prefix Product, Suffix Product, Matrix, Arrays, Optimization, Modular Arithmetic, DSA Practice, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #Matrix #PrefixSum #Optimization #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep

🚀 Day 29 of 100 Days LeetCode Challenge Problem: Check if Strings Can be Made Equal With Operations I Day 29 is a short but pattern + constraint observation problem 🔥 💡 Key Insight: We can only swap characters where: 👉 j - i = 2 For a string of length 4, possible swaps: Index 0 ↔ 2 Index 1 ↔ 3 👉 That means: Positions (0,2) form one group Positions (1,3) form another group 🔍 Core Approach: 1️⃣ Group Characters Extract characters from: Even indices → [0, 2] Odd indices → [1, 3] 2️⃣ Compare Groups Sort both groups for s1 and s2 If both corresponding groups match → ✅ true Else → ❌ false 💡 Why This Works: You can rearrange freely within each group But cannot mix between groups 🔥 What I Learned Today: Limited operations define independent groups Think in terms of index grouping Small problems still test logical clarity 📈 Challenge Progress: Day 29/100 ✅ One day to 30! LeetCode, Strings, Swapping, Greedy, Pattern Recognition, Arrays, DSA Practice, Coding Challenge, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #Strings #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep

🚀 LeetCode Update: “Sort Colors” Problem Solved! I recently solved the **Sort Colors** problem and got it accepted ✅ (89/89 test cases passed). Here’s a quick breakdown of my approach 👇 🧠 Problem Insight • The array contains only 0s, 1s, and 2s • Goal: sort them in-place without using extra space ⚙️ Approach Used: Dutch National Flag Algorithm • Maintained three pointers: low, mid, high • Divided the array into three regions: * 0s → left side * 1s → middle * 2s → right side • Traversed the array once and swapped elements accordingly 📈 Time & Space Complexity • Time Complexity: O(n) • Space Complexity: O(1) (in-place sorting) 💡 Key Learning • Efficient use of pointers can eliminate the need for extra space • Classic problems often have optimal patterns worth mastering 🔥 Always exciting to see how a simple-looking problem can teach powerful concepts! #LeetCode #DSA #CodingJourney #Cpp #ProblemSolving

🚀 Day 17 of 100 Days LeetCode Challenge Problem: Largest Submatrix With Rearrangements Today’s problem is a powerful mix of matrix + greedy + sorting optimization 🔥 💡 Key Insight: We are allowed to rearrange columns, which changes everything! 👉 Instead of fixed positions: Focus on heights of consecutive 1’s in each column 🔍 Core Approach: 1️⃣ Build Heights Matrix For each cell: If 1 → increase height from previous row If 0 → reset to 0 👉 This converts the problem into a histogram per row 2️⃣ Sort Each Row (Greedy Move) Sort heights in descending order Why? → To maximize width for larger heights 3️⃣ Calculate Max Area For each position j: Area = height[j] × (j + 1) Track maximum across all rows 🔥 What I Learned Today: Rearrangement problems → think flexibility optimization Converting matrix → histogram simplifies logic Sorting can unlock hidden maximums 📈 Challenge Progress: Day 17/100 ✅ Strong consistency streak! LeetCode, Matrix, Greedy Algorithm, Sorting, Histogram, Optimization, DSA Practice, Coding Challenge, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #Matrix #GreedyAlgorithm #Sorting #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep

🚀 Day 14 of 100 Days LeetCode Challenge Problem: The K-th Lexicographical String of All Happy Strings of Length n Today’s problem is a perfect blend of Backtracking + Lexicographical Ordering 🔥 💡 Key Insight: A happy string: Uses only 'a', 'b', 'c' No two adjacent characters are the same 👉 Instead of generating all strings blindly, we: Build valid strings using backtracking Maintain lexicographical order naturally 🔍 Core Approach: 1️⃣ Backtracking (DFS) Start building string character by character At each step: Choose from 'a', 'b', 'c' Skip if same as previous character 2️⃣ Lexicographical Order Always try characters in order: 'a' → 'b' → 'c' 3️⃣ Stop Early Once we reach the k-th string, stop recursion 👉 If total strings < k → return "" 🔥 What I Learned Today: Backtracking is powerful for constraint-based generation Ordering decisions early helps avoid extra sorting Early stopping = major optimization 📈 Challenge Progress: Day 14/100 ✅ 2 weeks strong! LeetCode, Backtracking, Recursion, Lexicographical Order, Strings, DFS, DSA Practice, Coding Challenge, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #Backtracking #Recursion #Strings #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep

🚀 Day 16 of 100 Days LeetCode Challenge Problem: Get Biggest Three Rhombus Sums in a Grid Today’s problem was a matrix + geometry + prefix sum optimization challenge 🔥 💡 Key Insight: A rhombus is basically a rotated square, and we only need the border sum, not the entire area. 👉 Brute force works, but it’s slow. So we optimize using diagonal prefix sums. 🔍 Core Approach: 1️⃣ Understand Rhombus Shape Defined by a center and a “radius” Four edges → top, right, bottom, left 2️⃣ Efficient Border Sum Use diagonal prefix sums to quickly calculate edges Avoid recomputing each cell repeatedly 3️⃣ Track Top 3 Unique Sums Use a set or priority structure Keep only the largest 3 distinct values 🔥 What I Learned Today: Geometry-based problems require visual thinking Prefix sums are powerful beyond simple arrays Optimization matters when dealing with nested loops 📈 Challenge Progress: Day 16/100 ✅ Still consistent, still growing! LeetCode, Matrix, Prefix Sum, Geometry, Optimization, Arrays, DSA Practice, Coding Challenge, Problem Solving #100DaysOfCode #LeetCode #DSA #CodingChallenge #Matrix #PrefixSum #ProblemSolving #TechJourney #ProgrammerLife #SoftwareDeveloper #CodingLife #LearnToCode #Developers #Consistency #GrowthMindset #InterviewPrep