Mobile numeric keypad | GfG POTD | 27-06-2025 | GfG Problem of the day | GeeksforGeeks

Today’s GfG POTD: Mobile Numeric Keypad
GfG Link → https://www.geeksforgeeks.org/problems/mobile-numeric-keypad5456/1
Code → https://github.com/imnilesh18/GfG-POTD/blob/master/06_June/27_Mobile%20numeric%20keypad.cpp

⏱ Video Chapters
00:00 Introduction
0:29 Problem Statement & Constraints
04:52 Building Intuition & Key Observations
05:45 Recursion
08:28 Code

🔑 Primary Keywords
MobileNumericKeypad, GfGPOTD, DynamicProgramming, Memoization, Recursion, GridTraversal, TopDownDP, GeekStreak2025, LeetGeek, GeeksforGeeks, CodingInterviewPrep

🧾 Problem Statement
Given an integer n, determine how many unique sequences of length n can be formed by pressing buttons on a standard 4×3 mobile keypad. From each key you can stay in place or move up/down/left/right (no diagonals, and * / # are forbidden). Return the total count of valid sequences.

📊 Example Inputs & Outputs

Input: n = 1 → Output: 10
Explanation: Each digit alone: 0→0, 1→1, …, 9→9.

Input: n = 2 → Output: 36
Explanation: From 5: “55”, “25”, “45”, “65”, “85” (5 ways); sum over all starting keys gives 36.

🧠 What You’ll Learn

How to map a keypad to a 4×3 grid and handle forbidden cells
Top-down DP with memoization to avoid redundant recursion
Recurrence: dp[i][j][len] = sum over stay + up/down/left/right
Handling base cases and invalid moves
Time Complexity O(12·n), Space Complexity O(12·n)

Line-by-line C++ & Java implementations
Dry run to solidify your understanding

📂 Resources & Code
GfG POTD Problem: https://www.geeksforgeeks.org/problems/mobile-numeric-keypad5456/1
GitHub Solutions (C++ & Java): https://github.com/imnilesh18/GfG-POTD/blob/master/06_June/27_Mobile%20numeric%20keypad.cpp
Full Repository: https://github.com/imnilesh18/GfG-POTD

🚀 Why Watch?
• Master a classic DP pattern on grids with memoization
• Two language implementations side-by-side
• Clear dry runs to build intuition
• Perfect for GeeksforGeeks streaks and interviews

👍 If this helped, Like, drop your questions below 💬, and Subscribe 🔔 to LeetGeek for daily GfG POTD tutorials!

🔖 Tags
#MobileNumericKeypad #NumericKeypadDP #GridDP #MemoizationTechnique #TopDownDP #RecursiveDP #GeeksforGeeksTutorial #GfGPOTD #LeetGeek #GeekStreak2025 #CodingInterviewQuestions #DynamicProgramming #Recursion #DPGrid #MobileKeypadProblem #CPlusPlusDP #JavaDP #InterviewPrep #CompetitiveProgramming #AlgorithmDesign #TimeComplexity #SpaceComplexity #KeypadSequences #ForbiddenCells #MoveValidation #DryRunExample #CodeWalkthrough #StepByStepExplanation #EducationalVideo #TechEducation #SoftwareEngineering #ProblemSolving #PracticeCoding #AlgorithmTutorial #YouTubeLearning #CodingChallenge #DailyCodingChallenge #GfGProblemOfTheDay #SequenceCounting #DPOptimization #MemoTable #BaseCaseHandling #EdgeCaseDiscussion #ExampleWalkthrough #VideoTutorial #ClearIntuition #CodeImplementation #GitHubResources #FullRepositoryLink #SubscribeNow #DailyGfGTutorials #CodingTips #DataStructures #AlgorithmInsights #PriorityQueue #BucketStrategy #GreedyAlgorithm #FrequencySquares #StringAlgorithms #HashMapTechnique #FrequencyMap #SquareSum #ProblemAnalysis #SolutionPatterns #LearningAlgorithms #TutorialVideo #EducationalContent #InterviewPrepTips #SoftwareDev

Видео Mobile numeric keypad | GfG POTD | 27-06-2025 | GfG Problem of the day | GeeksforGeeks канала LeetGeek