Question

Implement the \void enqueue(int val)" function in the QueueUsingStack.java/QueueUsingStack.h file (ATTACHED BELOW). Here are some hints on how to implement this using two stacks:

- Create a stack \tempStack", which has the same maximum capacity as the mainStack.

- Pop all numbers from mainStack and push them onto tempStack.

- Push the new number onto mainStack.

- Pop all numbers from tempStack and push them onto mainStack.

Implement the \int dequeue()" function in the QueueUsingStack.java/QueueUsingStack.h le. Recall that this is nothing but a pop on the mainStack.

Implement the \int getSize()" function in the QueueUsingStack.java/QueueUsingStack.h le. Recall that this is nothing but the size of mainStack.

public class QueueUsingStack {
  
Stack mainStack;
int maxQueueSize;
  
public QueueUsingStack(int maxQueueSize) {
this.maxQueueSize = maxQueueSize;
mainStack = new Stack(maxQueueSize);
}
  
public void enqueue(int val) { // complete this function
}
  
public int dequeue() { // complete this function
}
  
public int getSize() { // complete this function
}
  
public String toString() {
if (getSize() == 0) {
return "[]";
} else {
String output = "[";
int n = getSize();
for (int i = 0; i < n - 1; i++) {
int x = dequeue();
output += x + ", ";
enqueue(x);
}
int x = dequeue();
output += x + "]";
enqueue(x);
return output;
}
}
}

Answer 1

import java.util.Stack;

public class QueueUsingStack {

Stack mainStack;

Stack s2;

int maxQueueSize;

public QueueUsingStack(int maxQueueSize) {

this.maxQueueSize = maxQueueSize;

mainStack = new Stack();
s2 = new Stack();

}

public void enqueue(int val) { // complete this function

while (!mainStack.isEmpty()) {

s2.push(mainStack.pop());

}

mainStack.push(val);

while (!s2.isEmpty()) {

mainStack.push(s2.pop());

}

}

public int dequeue() { // complete this function

if (mainStack.isEmpty()) {

System.out.println("Queue is Empty");

return -1;

}

int answer = (int) mainStack.peek();

mainStack.pop();

return answer;

}

public int getSize() { // complete this function

return mainStack.size();

}

public String toString() {

if (getSize() == 0) {

return "[]";

} else {

String output = "[";

int n = getSize();

for (int i = 0; i < n - 1; i++) {

int x = dequeue();

output += x + ", ";

enqueue(x);

}

int x = dequeue();

output += x + "]";

enqueue(x);

return output;

}

}

}