2.Given an array of integers, you have to find all pairs of elements in this array such that whose sum must be equal to a given number. For example, if {4, 5, 7, 11, 9, 13, 8, 12} is an array and 20 is the given number, then you have to find all pairs of elements in this array whose sum must be 20. In this example, (9, 11), (7, 13) and (8, 12) are such pairs whose sum is 20.

3.Given 3 int values, a b c, return their sum. However, if one of the values is 13 then it does not count towards the sum and values to its right do not count. So for example, if b is 13, then both b and c do not count. luckySum(1, 2, 3) → 6 luckySum(1, 2, 13) → 3 luckySum(1, 13, 3) → 1

4.oops concept,JSP, servlets,sql query (joins imp) ,collectins ,spring,hibernate etc.

Return the sum of the numbers in the array, returning 0 for an empty array. Except the number 13 is very unlucky, so it does not count and numbers that come immediately after a 13 also do not count. sum13([1, 2, 2, 1]) → 6 sum13([1, 1]) → 2 sum13([1, 2, 2, 1, 13]) → 6