Basic Data structure questions

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Which data structure is used in redo-undo feature?

Explanation:  Stack data structure is most suitable to implement redo-undo feature. This is because the stack is implemented with LIFO(last in first out) order which is equivalent to redo-undo feature i.e. the last re-do is undo first. Consider a situation where a client receives packets from a server. There may be differences in speed of the client and the server. Which data structure is best suited for synchronization? (A)  Circular Linked List (B)  Queue (C)  Stack (D)  Priority Queue Answer:   (B) Explanation:  Since packets need to be processed in First In First Out order, a queue can be used for synchronization. A data structure is required for storing a set of integers such that each of the following operations can be done in (log n) time, where n is the number of elements in the set. o Delection of the smallest element o Insertion of an element if it is not already present in the set Which of the following data structur...
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Print all subsets of given size of a set

Generate all possible subset of size  r  of given array with distinct elements. Examples: Input : arr[] = {1, 2, 3, 4} r = 2 Output : 1 2 1 3 1 4 2 3 2 4 3 4 Input : arr[] = {10, 20, 30, 40, 50} r = 3 Output : 10 20 30 10 20 40 10 20 50 10 30 40 10 30 50 10 40 50 20 30 40 20 30 50 20 40 50 30 40 50 The idea here is similar to  Subset Sum Problem . We one by one consider every element of input array, and recur for two cases: 1) The element is included in current combination (We put the element in data[] and increment next available index in data[]) 2) The element is excluded in current combination (We do not put the element and do not change index) When number of elements in data[] become equal to r (size of a combination), we print it. This method is mainly based on  Pascal’s Identity , i...
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[23] Find top k (or most frequent) numbers in a stream

Given an array of n numbers. Your task is to read numbers from the array and keep at-most K numbers at the top (According to their decreasing frequency) every time a new number is read. We basically need to print top k numbers sorted by frequency when input stream has included k distinct elements, else need to print all distinct elements sorted by frequency. Examples: Input :  arr[] = {5, 2, 1, 3, 2}              k = 4 Output : 5 2 5 1 2 5 1 2 3 5 2 1 3 5 Input  : arr[] = {5, 2, 1, 3, 4}              k = 4 Output : 5 2 5 1 2 5 1 2 3 5 1 2 3 4 Expected time complexity is O(n * k) Given an array of n numbers. Your task is to read numbers from the array and keep at-most K numbers at the top (According to their decreasing frequency) every time a new number is read. We basically need to print top k numbers sorted by frequency when input stream has included k distinct elements, else need to print all...
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