Wells Fargo Software Developer interview questions

1)Write a program to print the count of unique BSTs given 'n' nodes (0-n values in the nodes). 2)Difference between Java and C++ 3)What happens when a url is typed in a browser? (Request flow) 4)What is semaphore? 5)What is trie?

i) Given an array with duplicate values, find the number of pairs that have a difference equal to a given integer number. The array can contain duplicate values. The input consists of a number ‘N’ giving the size of the array and a number ‘D’ which gives the difference. The next line consists of N space separated integers. Input : 7 6 2 3 3 5 9 15 15 Output : 4 Explanation : The pairs are {3,9},{3,9},{9,15},{9,15} = 4