Pergunta de entrevista da empresa Oracle

first technical interview tell me about yourself? which language are you comfortable in for coding? given a large array ,program to count frequency of each number in an optimized way? program for multiplication of two numbers consists of 20 digits each? given almost a postfix expression,program to get the result? given a excel sheet,get the column number of ABCD and column name of 6532? when all the numbers of different combinations consisting of 1,2,3,4,5 are arranged in increasing order,give the rank of number 35421 ? given an array of positive and negative numbers,arrange them in such a way that all positive numbers at one end and negative numbers at other end(size of array is large and unknown) about projects all solutions should be optimized