C Interview Questions

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Try to solve 6 C interview questions below. Hints can help you find answers to questions you are having trouble with.

1. Words

Algorithmic thinking Sorting
   
Easy  

Implement function sort_words that sorts an array of words that contain lowercase characters from english alphabet, in descending order, and is efficient with respect to time used.

For example, the array { "cherry", "orange", "apple" } should, after sorting, become { "orange", "cherry", "apple" }.

C  
 


  •   Example case: Wrong answer
  •   Several words: Wrong answer
  •   Performance test on a dictionary: Wrong answer


2. Binary Search Tree

Algorithmic thinking Recursion Tree
   
Easy  

Binary search tree (BST) is a binary tree where the value of each node is larger or equal to the values iA three-node binary tree.n all the nodes in that node's left subtree and smaller than the values in all the nodes in that node's right subtree.

Write a function that, efficiently with respect to time used, returns 1 if a given binary search tree contains a given value, else 0.

For example, for the following tree:

  • n1 (Value: 1, Left: null, Right: null)
  • n2 (Value: 2, Left: n1, Right: n3)
  • n3 (Value: 3, Left: null, Right: null)

Call to contains(&n2, 3) should return 1 since a tree with root at n2 contains number 3.

C  
 


  •   Example case: Wrong answer
  •   Correctness: Wrong answer
  •   Performance test on a large tree: Wrong answer


3. Inspect Bits

Bit manipulation
   
Easy  

Implement the inspect_bits function that checks if given number contains 2 or more consecutive ones in its binary representation. If it does, the function should return 1. Otherwise, it should return 0.

For example, inspect_bits(13) should return 1 as it contains 2 consecutive ones in its binary representation (1101).

C  
 


  •   Example case: Wrong answer
  •   Various numbers: Wrong answer


4. Quadratic Equation

Arithmetic
   
Easy 

Implement the function find_roots to find the roots of the quadratic equation: ax2 + bx + c = 0. If the equation has only one solution, the function should return that solution as both roots. The equation will always have at least one solution.

The roots of the quadratic equation can be found with the following formula: A quadratic equation.

For example, the roots of the equation 2x2 + 10x + 8 = 0 are -1 and -4.

C  
 


  •   Sample case: Wrong answer
  •   Integer roots: Wrong answer
  •   Real roots: Wrong answer


5. Watched Videos

Arrays Pointers
   
Easy 

Implement the count_views function. It accepts an array of pointers to the Viewer struct, the size of the array, and the character array with the video name. It should return the number of Viewers who have watched a Video with the name video_name.

For example,

Video videos[] = { {.name = "Soccer", .unique_views = 500},
                   {.name = "Basketball", .unique_views = 1000} };
Viewer viewer = {.username = "Dave", .watched_videos = videos,
                 .watched_videos_size = 2};    
Viewer *viewers[] = { &viewer };

calling count_views(viewers, 1, "Soccer") should return 1.

C  
 


  •   Example case: Wrong answer
  •   Some people did not see the video: Wrong answer
  •   Various people and videos: Wrong answer
  •   Strings are dynamically allocated: Wrong answer


6. User Info

Data structure alignment Memory management
   
Hard 

Consider the struct UserInfo, which is used in a performance critical sub-system.

Currently, on a system where an int takes 4 bytes, char takes 1 byte and long long takes 8 bytes, the struct takes 40 bytes of space. Rearrange the struct, without removing, renaming, or changing the type of the members, so that it uses less memory. The code uses pointers to struct members, so struct should be properly aligned.

C  
 


  •   The UserInfo struct takes less than 40 bytes of memory: Wrong answer
  •   The UserInfo struct takes less than 25 bytes of memory: Wrong answer
  •   The UserInfo struct is properly aligned: Wrong answer


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