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Added "peek" function for QueueUsingTwoStacks #282

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Merged
merged 1 commit into from
Oct 27, 2017
Merged

Added "peek" function for QueueUsingTwoStacks #282

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21 changes: 21 additions & 0 deletions Others/QueueUsingTwoStacks.java
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Original file line number Diff line number Diff line change
Expand Up @@ -55,6 +55,21 @@ public Object remove() {
return this.outStack.pop();
}

/**
* Peek at the element from the front of the queue
*
* @return the new front of the queue
*/
public Object peek() {
if(this.outStack.isEmpty()) {
// Move all elements from inStack to outStack (preserving the order)
while(!this.inStack.isEmpty()) {
this.outStack.push( this.inStack.pop() );
}
}
return this.outStack.peek();
}

/**
* Returns true if the queue is empty
*
Expand Down Expand Up @@ -101,18 +116,24 @@ public static void main(String args[]){
// outStack: [(top) 2, 3, 4]

myQueue.insert(5);
System.out.println(myQueue.peek()); //Will print 2
// instack: [(top) 5]
// outStack: [(top) 2, 3, 4]

myQueue.remove();
System.out.println(myQueue.peek()); //Will print 3
// instack: [(top) 5]
// outStack: [(top) 3, 4]
myQueue.remove();
System.out.println(myQueue.peek()); //Will print 4
// instack: [(top) 5]
// outStack: [(top) 4]
myQueue.remove();
// instack: [(top) 5]
// outStack: []
System.out.println(myQueue.peek()); //Will print 5
// instack: []
// outStack: [(top) 5]
myQueue.remove();
// instack: []
// outStack: []
Expand Down