50) Which of the following permutations can be obtained in the output(in the same order),using a stack assuming that the input is the sequence 1,2,3,4,5 in that order?

51) Stack is useful for implementing

52) If the sequence of operations- push (1), push (2), pop, push (1), push (2), pop, pop, pop, push (2), pop, are performed on a stack, the sequence of popped out values are

53) Stack A has the entries a, b, c (with a on top), Stack B is empty. An entry popped out of stack A can be printed immediately or pushed to stack B. An entry popped out of stack B can only be printed. In the arrangement, which of the following permutations of a, b, c is not possible?

54) The postfix equivalent of the prefix * + a b - c d is