# Basic CS-Data Structures [3i Infotech Placement]: Sample Questions 1 - 3 of 52

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## Question 1

Data Structures
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### Describe in Detail

Essay▾

What is a hash table? When would you can use one?

### Explanation

• Value is stored in a data structure called hash table.
• Uses a hash function to compute an index into an array which element will search.
• Also used with key/value pairs to store and retrieve value using key.
• Hash table access of data becomes very fast if we know the index of the desired data.
• The average time required to search for an element in a hash table is O (1) .
• Basic operation of hash table:
• Search: search an element in a hash table.
• Insert: insert an element in a hash table.
• Delete: Delete an element from a hash table.

## Question 2

Data Structures
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### Write in Short

If a binary tree has 20 nodes then it has how many null branches?

### Explanation

• A binary tree with 20 nodes has 21 many null branches.
• Consider, a tree with 5 nodes (n = 5)
• No. of null pointer = 2n- (n-1) = n + 1
• When , n = 20
• Then n + 1 = 20 + 1 = 21

Data Structures
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