Java 8 solutions of interview tasks:

• Plane seats reservation - Solution1.java

The plane has N rows of seats (1 ... N). There are 10 seats in each row (from A to K - no letter I is used).

row	A	B	C		D	E	F	G		H	J	K
1				X					X
2				X					X
.........
N				X					X

An example string S = "2B 7E 3K" can represent taken seats in arbitrary order.

The method public int solution(int N, String S), where N is number of rows and S in string of taken seats mentioned above, returns the maximum number of 3-persons families that can be seated without separation (either by new row or by corridor between seats C&D or G&H).

The JUnit tests are placed in TestSolution1.java.

• Main elements of the table - Solution2.java

Definitions:

1. the main element of an array is element which occures more then half times in the array
2. the segemnt of an array is a sequence of consecutive elements

The method public int[] solution(int K, int M, int[] A) returns a table of all elements which can become a main element, after increasing by 1 every element of exactly one segment of A of length K (table A consist of integers not bigger then M). The returend array is ASC ordered without duplication.

• The word machine - Solution3.java

The word machine performs a sequence of simple operations on a stack of integers. Operations are given as a string, separated by single spaces. There are five types of operations:

• an integer between 0 and 2²⁰ - 1; machine pushes it onto the stack
• "POP" : removes topmost number from stack
• "DUP" : duplicate the topmost number onto the stack
• "+" : pops two topmost numbers, adds them and pushes the sum onto the stack
• "-" : pops two topmost numbers, substracts second one from the first and pushes the difference onto the stack.

After processing all operations, machine returns topmost value from the stack.

Posible errors:

• overflow (>2²⁰ -1) or underflow (<0) errors
• an error when the machine operations needs more numbers than is currently on the stack
• an error when the stack is empty after performing all operations - nothing to return

The result function returns -1 in case of an error.

For example, an input string 13 DUP 4 POP 5 DUP + DUP + - causes the result function public int solution(String S) to return 7.

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I found task to be difficult in ascending order as : (the easiest) 3 , 1, 2 (the most dififcult).