You are on level: Student
Overview
Quick DSA Review
Basic Algorithms
Sorted Array
Implicitly Sorted Array
Advanced
Speedrun
Core Concepts
Same Direction
Opposite Direction
Sliding Window
Cycle Finding
Decision Making
Introduction
DFS on Tree
Binary Search Tree
Combinatorial Search
Additional States
Aggregation and Memoization
Additional Practices
Speedrun
Introduction
Vanilla BFS
Matrix as Graph
Implicit Graph
Directed Graph / Topological Sort
Weighted Graph
Minimum Spanning Tree
Introduction
Top K
Moving Best
Multiple Heaps
Introduction
Constant Transition
Grid
Dual-Sequence
Non-constant Transition
Knapsack, Weight-Only
Knapsack, Weight+Value
Topological Sort
Additional Practices
Disjoint Set Union | Union Find
Data Structure Design
Segment Tree
Line Sweep
Tree Traversal without Recursion
Amazon OA
Microsoft OA
Google OA
Prereq: Memoization Intro
We have a message consisting of digits 0-9 to decode. Letters are encoded to digits by their positions in the alphabet
A -> 1 B -> 2 C -> 3 ... Y -> 25 Z -> 26
Given a non-empty string of digits, how many ways are there to decode it?
Input: "18"
Output: 2
Explanation: "18" can be decoded as "AH" or "R"
Input: "123"
Output: 3
Explanation: "123" can be decoded as "ABC", "LC", "AW"