// Demonstrates basic usage of stacks and queues
import java.util.*;

public class StacksQueues {
    public static void main(String[] args) {
        // Queue operations.
        Queue<Integer> q = createRandomQueue(10);
        System.out.println("q = " + q);
        int sum = sum(q);
        System.out.println("sum = " + sum);
        System.out.println("q = " + q);

        Stack<Integer> s = new Stack<Integer>();
        queueToStack(q, s);
        System.out.println("   after q->s: q = " + q);
        System.out.println("   after q->s: s = " + s);
        
        // Same with the stack
        Stack<Integer> s2 = createRandomStack(10);
        System.out.println("s = " + s2);
        int sum2 = sum(s2);
        System.out.println("sum = " + sum2);
        System.out.println("s = " + s2);
        
        Queue<Integer> q2 = new LinkedList<Integer>();
        stackToQueue(q2, s2);
        System.out.println("   after q->s: s = " + s2);
        System.out.println("   after q->s: q = " + q2);
   	}
    
	// pre: size >= 0
    // Creates and returns a queue with the specified number of random values
	// in the range 0-29.
    public static Queue<Integer> createRandomQueue(int size) {
        Queue<Integer> q = new LinkedList<Integer>();
        
        Random rand = new Random();
        for (int i = 0; i < size; i++) {
            q.add(rand.nextInt(30));
        }
        return q;
    }
    
    // post: Values from q moved to s (added in queue order, front to back)
    public static void queueToStack(Queue<Integer> q, Stack<Integer> s) {
        while (!q.isEmpty()) {
            int n = q.remove();
            s.push(n);
        }
    }
    
    // post: returns the sum of the values in the given queue
    public static int sum(Queue<Integer> q) {
        int sum = 0;
        
        for (int i = 0; i < q.size(); i++) {
            int n = q.remove();
            sum += n;
            q.add(n);
        }   
        
        return sum;
    }
    
    
	// pre: size >= 0
    // Creates and returns a stack with the specified number of random values
	// in the range 0-29.
    public static Stack<Integer> createRandomStack(int size) {
        Stack<Integer> s = new Stack<Integer>();
        
        Random rand = new Random();
        for (int i = 0; i < size; i++) {
            s.push(rand.nextInt(30));
        }
        return s;
    }
    
    // post: Values from s moved to q (added in stack order, top to bottom);
    public static void stackToQueue(Queue<Integer> q, Stack<Integer> s) {
        while (!s.isEmpty()) {
            int n = s.pop();
            q.add(n);
        }
    }
    
    // post: returns the sum of the values in the given stack
    public static int sum(Stack<Integer> s) {
        int sum = 0;
        Queue<Integer> q = new LinkedList<Integer>();
        int size = s.size();
        for (int i = 0; i < size; i++) {
            int n = s.pop();
            sum += n;
            q.add(n);
        }
        queueToStack(q, s);
        stackToQueue(q, s);
        queueToStack(q, s);
        return sum;
    }
}