(adapted from 8.9) the input stream of a stack is a list of all the elements we pushed onto the stack, in the order that we pushed them. the input stream from exercise 8.8 on page 304 of the book for example is abcdefghijklm the output stream is a list of all the elements that are popped off the stack in the order that they are popped off. a. if the input stream is zyxwvutsr, create a sequence of pushes and pops such that the output stream is yxvuwzsrt. b. if the input stream is zyxw, how many different output streams can be created?