232. Implement Queue using Stacks && 225. Implement Stack using Queues

232. Implement Queue using Stacks

Implement the following operations of a queue using stacks.

• Push (x)--push element x to the back of the queue.
• Pop ()--Removes the element from in front of the queue.
• Peek ()--Get the front element.
• Empty ()--Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack--which means only push to top , peek/pop from top , size , and is empty operations AR E valid.
• Depending on your language, stack may is not supported natively. You could simulate a stack by using a list or deque (double-ended queue), as long as if you have standard operations of a s Tack.
• You may assume this all operations is valid (for example, no pop or peek operations would be called on an empty queue).

Stack Design

classMyqueue {Deque<Integer> stack =NewArraydeque<integer>(); //Push element x to the back of the queue.     Public voidPushintx) {//Organize at push stage becasue peek needs to see the top.deque<integer> temp =NewArraydeque<integer>();  while(!Stack.isempty ())        {Temp.push (Stack.pop ());        } stack.push (x);  while(!Temp.isempty ())        {Stack.push (Temp.pop ()); }    }    //Removes the element from in front of the queue.     Public voidpop () {stack.pop (); }    //Get the front element.     Public intPeek () {returnStack.peek (); }    //Return Whether the queue is empty.     Public Booleanempty () {returnStack.isempty (); }}

225. Implement Stack using Queues

Implement the following operations of a stack using queues.

• Push (x)-push element x onto stack.
• Pop ()--Removes the element on top of the stack.
• Top ()--Get the top element.
• Empty ()--Return whether the stack is empty.

Notes:

• You must the only standard operations of a queue – which means only push to back ,, peek/pop from front size , and is empty operations is Valid.
• Depending on your language, queue May is not supported natively. You could simulate a queue by using a list or deque (double-ended queue), as long as if you have standard operations of a Q Ueue.
• You may assume this all operations is valid (for example, no pop or top operations would be called on an empty stack).

Update (2015-06-11):
The class name of the Java function had been updated to Mystack instead of Stack.

Stack Design

classMystack {Deque<Integer> queue =NewArraydeque<integer>(); //Push element x onto stack.     Public voidPushintx) {queue.add (x);  for(intI=0;i<queue.size () -1;i++) {Queue.add (Queue.poll ()); }    }    //removes the element on top of the stack.     Public voidpop () {queue.poll (); }    //Get the top element.     Public intTop () {returnQueue.peek (); }    //Return Whether the stack is empty.     Public Booleanempty () {returnQueue.isempty (); }}

232. Implement Queue using Stacks && 225. Implement Stack using Queues