Basic stuff in Problem solving

Some popular Competitive challenge contests I know..

Tcs           - Codevita
Infosys       - HackWithInfy
GOLDMAN SACHS - GOLDMAN SACHS 
Google        - Google'sCode Jam
Google        - APAC
Facebook      - Hacker Cup
Microsoft     - Imagine Cup 
ACM           - ICPC
Codechef      - SnackDown

and more..

Some useful topics...

 °Greedy Algorithm
 °Stack
 °Queue
 °Mapping Concepts
 °Array manipulation
 °String manipulation
 °Tree
 °Dynamic Programming
 °BackTracking
 °Graph

In most cases divide and conquer works well.
Every exam has its own pattern.

For instance,in Tcs codevita,
6 Coding questions will be asked and the difficulty increases as we move from question 1 to question 6 . 1st question does not involve any dynamic programming or difficult algorithm , but , will be on simple mathematics, and simple problem solving skills. It's well-known that

 TCS hires its digital 
 candidates from Codevita.

FYI, Many got an interview opportunity for solving 2-3 questions

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Which programming language is best for problem solving ?

Every programming language has its own unique capabilities, features, services etc
In any programming language we can solve the problems .

  Proceed using the 
  programming language in 
  which you are most 
  comfortable with.

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Usually...

 For beginners , python is 
 recommended in most cases.

Because,easy to Learn, Read, and Use .Unlike C++ or C# or java and other languages, Python's syntax is human readable and it's concise. As a beginner, this will allow you pick up the basics quickly, with less mental strain, and you can level up to advanced topics quicker. With one glance at Python code, you can infer what the code is doing.