These websites are suitable for beginners as they've problems in sorted order as required by beginners.
This is a series of 7 questions/tutorials which will help the newbie to adapt to the competitive coding environment.
- Hackerearth Practice
They've 3 major sub categories --
In this just have a look on Basics of Input/Output and move to next category.
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Data Structures
It has all the basic things covered eg.1. Arrays * 1-D * Multi-dimensional 2. Stacks * Basics of Stacks 3. Queues * Basics of Queues 4. Hash Tables * Basics of Hash Tables 5. Linked List * Singly Linked List 6. Trees * Binary/ N-ary Trees * Binary Search Tree * Heaps/Priority Queues 7. Advanced Data Structures ... 8. Disjoint Data Structures ...You've to go through the questions of these categories before moving to the next category.
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Algorithms
They've covered all the common algorithms and some advanced too (you can skip the advanced ones)1. Searching * Linear Search * Binary Search * ... 2. Sorting * Bubble Sort * Selection Sort * Insertion Sort * Merge Sort * Quick Sort * ... * Heap Sort * ... 3. Greedy Algorithms * Basics of Greedy Algorithms 4. Graphs * Breadth First Search * Depth First Search * Minimum Spanning Tree * Shortest Path Algorithms 5. Dynamic Programming * Introduction to Dynamic Programming 1
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- Hackerrank - Datastructure
- Hackerrank - Algorithms
When in problem refer
Always start competitive programming in pairs/groups, it'll help go a long way.