Java - BJP3 Exercise 14.4: collapse Write a method collapse that takes a stack o

Question

Java - BJP3 Exercise 14.4: collapse

Write a method collapse that takes a stack of integers as a parameter and that collapses it by replacing each successive pair of integers with the sum of the pair. For example, suppose a stack stores these values:

The first pair should be collapsed into 9 (7 + 2), the second pair should be collapsed into 17 (8 + 9), the third pair should be collapsed into 17 (4 + 13) and so on to yield:

If the stack stores an odd number of elements, the final element is not collapsed. For example, the stack:

Would collapse into:

With the 5 at the top of the stack unchanged. You may use one queue as auxiliary storage.

Explanation / Answer

public void collapse(Stack<Integer>s)

{

Queue<Integer>q = new LinkedList<Integer>();

for(i=0;i<=s.size;i++)

q.enqueue(s.pop());

while(!q.dequeue())

s.push(q.dequeue());

while(!s.isEmpty())

q.enqueue(s.pop());

while(q.size()>1)

s.push(q.dequeue()+q.dequeue());

if(!q.isEmpty())

s.push(q.dequeue());

}

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