Arrays

Exercises from book "Fundamentals of Computer Programming with C#" Exercise 7: Arrays

1. Write a program, which creates an array of 20 elements of type integer and initializes each of the elements with a value equals to the index of the element multiplied by 5. Print the elements to the console.

2. Write a program, which reads two arrays from the console and checks whether they are equal (two arrays are equal when they are of equal length and all of their elements, which have the same index, are equal).

3. Write a program, which compares two arrays of type char lexicographically (character by character) and checks, which one is first in the lexicographical order.

4. Write a program, which finds the maximal sequence of consecutive equal elements in an array. E.g.: {1, 1, 2, 3, 2, 2, 2, 1}  {2, 2, 2}.

5. Write a program, which finds the maximal sequence of consecutively placed increasing integers. Example: {3, 2, 3, 4, 2, 2, 4}  {2, 3, 4}.

6. Write a program, which finds the maximal sequence of increasing elements in an array arr[n]. It is not necessary the elements to be consecutively placed. E.g.: {9, 6, 2, 7, 4, 7, 6, 5, 8, 4}  {2, 4, 6, 8}.

7. Write a program, which reads from the console two integer numbers N and K (K<N) and array of N integers. Find those K consecutive elements in the array, which have maximal sum.

8. Sorting an array means to arrange its elements in an increasing (or decreasing) order. Write a program, which sorts an array using the algorithm "selection sort".

9. Write a program, which finds a subsequence of numbers with maximal sum. E.g.: {2, 3, -6, -1, 2, -1, 6, 4, -8, 8}  11

10. Write a program, which finds the most frequently occurring element in an array. Example: {4, 1, 1, 4, 2, 3, 4, 4, 1, 2, 4, 9, 3}  4 (5 times).

11. Write a program to find a sequence of neighbor numbers in an array, which has a sum of certain number S. Example: {4, 3, 1, 4, 2, 5, 8}, S=11  {4, 2, 5}.

12. Write a program, which creates square matrices like those in the figures below and prints them formatted to the console. The size of the matrices will be read from the console. See the examples for matrices with size of 4 x 4 and make the other sizes in a similar fashion:

13. Write a program, which creates a rectangular array with size of n by m elements. The dimensions and the elements should be read from the console. Find a platform with size of (3, 3) with a maximal sum.

14. Write a program, which finds the longest sequence of equal string elements in a matrix. A sequence in a matrix we define as a set of neighbor elements on the same row, column or diagonal.

15. Write a program, which creates an array containing all Latin letters. The user inputs a word from the console and as result the program prints to the console the indices of the letters from the word.

16. Write a program, which uses a binary search in a sorted array of integer numbers to find a certain element.

17. Write a program, which sorts an array of integer elements using a "merge sort" algorithm.

18. Write a program, which sorts an array of integer elements using a "quick sort" algorithm.

19. Write a program, which finds all prime numbers in the range [1…10,000,000].

20. * Write a program, which checks whether there is a subset of given array of N elements, which has a sum S. The numbers N, S and the array values are read from the console. Same number can be used many times. Example: {2, 1, 2, 4, 3, 5, 2, 6}, S = 14  yes (1 + 2 + 5 + 6 = 14)

21. Write a program which by given N numbers, K and S, finds K elements out of the N numbers, the sum of which is exactly S or says it is not possible. Example: {3, 1, 2, 4, 9, 6}, S = 14, K = 3  yes (1 + 2 + 4 = 14)

22. Write a program, which reads an array of integer numbers from the console and removes a minimal number of elements in such a way that the remaining array is sorted in an increasing order. Example: {6, 1, 4, 3, 0, 3, 6, 4, 5}  {1, 3, 3, 4, 5}

23. Write a program, which reads the integer numbers N and K from the console and prints all variations of K elements of the numbers in the interval [1…N]. Example: N = 3, K = 2  {1, 1}, {1, 2}, {1, 3}, {2, 1}, {2, 2}, {2, 3}, {3, 1}, {3, 2}, {3, 3}.

24. Write a program, which reads an integer number N from the console and prints all combinations of K elements of numbers in range [1 … N]. Example: N = 5, K = 2  {1, 2}, {1, 3}, {1, 4}, {1, 5}, {2, 3}, {2, 4}, {2, 5}, {3, 4}, {3, 5}, {4, 5}.

25. * Write a program, which finds in a given matrix the largest area of equal numbers. We define an area in the matrix as a set of neighbor cells (by row and column). Here is one example with an area containing 13 elements with equal value of 3: