Solutions to the Practice Problems#
Java Programs Using a Stack#
Here is the code using my name.
Stack<Character> name = new Stack<>(); name.push('R'); name.push('o'); name.push('s'); name.push('a'); name.push('n'); name.push('n'); name.push('a'); while (!name.empty()){ System.out.print(name.pop()); } System.out.println();
The stack would have been created:
Stack<Integer> banana = new Stack<>();and items added.
a.banana.push(banana.pop() * 2);
b.Integer holdTop = banana.pop(); Integer sum = holdTop + banana.peek(); banana.push(holdTop); banana.push(sum);
Order really matters.
import java.util.Stack; public class JavaStacks { public static void main(String[] args) { Stack<Integer> myData = new Stack<>(); Stack<Integer> helperStack = new Stack<>(); myData.push(12); myData.push(15); myData.push(19); helperStack.push(myData.pop()); //19 helperStack.push(myData.pop()); //15 helperStack.push(myData.pop()); //12 myData.push(4); myData.push(helperStack.pop()); //12 myData.push(helperStack.pop()); //15 myData.push(helperStack.pop()); //19 helperStack.push(myData.pop()); //19 helperStack.push(myData.pop()); //15 helperStack.push(myData.pop()); //12 helperStack.push(myData.pop()); //4 myData.push(3); myData.push(helperStack.pop()); //4 myData.push(helperStack.pop()); //12 myData.push(helperStack.pop()); //15 myData.push(helperStack.pop()); //19 myData.push(35); helperStack.push(myData.pop()); //35 myData.push(20); myData.push(helperStack.pop()); //35 myData.push(36); helperStack.push(myData.pop()); //36 helperStack.push(myData.pop()); //35 helperStack.push(myData.pop()); //20 helperStack.push(myData.pop()); //19 helperStack.push(myData.pop()); //15 myData.push(14); myData.push(helperStack.pop()); //15 myData.push(helperStack.pop()); //19 myData.push(helperStack.pop()); //20 myData.push(helperStack.pop()); //35 myData.push(helperStack.pop()); //36 myData.push(42); System.out.println("The final stack is " + myData); }//main }//class
Better code, from a readability standpoint.
import java.util.Stack;
public class JavaStacks {
public static void main(String[] args) {
Stack<Integer> myData = new Stack<>();
addSorted(12, myData);
addSorted(15, myData);
addSorted(19, myData);
addSorted(4, myData);
addSorted(3, myData);
addSorted(35, myData);
addSorted(20, myData);
addSorted(36, myData);
addSorted(14, myData);
addSorted(42, myData);
System.out.println("The final stack is " + myData);
}//main
/**
* Moves integers from the first stack onto the second stack (in
* reverse order) until the top of the first stack is less than the
* give number.
* @param num - the given integer
* @param fromStack - moving off the top of this stack
* @param toStack - moving onto the top of this stack
*/
public static void moveUntilLess(Integer num, Stack<Integer> fromStack,
Stack<Integer> toStack){
while (!fromStack.empty() && fromStack.peek() > num){
toStack.push(fromStack.pop());
}
}//moveUntilLess
/**
* Moves everything on the first stack to the top of the second stack,
* in reverse order.
* @param fromStack - moves out of here
* @param toStack - moves into here, in reverse order
*/
public static void moveAll(Stack<Integer> fromStack,
Stack<Integer> toStack){
while (!fromStack.empty()){
toStack.push(fromStack.pop());
}
}//moveAll
/**
* Adds an item to an Integer stack to maintain a sorted order. NOTE:
* the stack is assumed sorted to start with. This is not a sort method.
* This is a method to maintain a sorted stack, by inserting the number
* in the proper place. The sort is ascending, from bottom to top.
* @param num - the Integer to insert
* @param theStack - the sorted stack of Integers, ascending from
* from bottom to top
*/
public static void addSorted(Integer num, Stack<Integer> theStack){
Stack<Integer> helperStack = new Stack<>();
moveUntilLess(num, theStack, helperStack);
theStack.push(num);
moveAll(helperStack, theStack);
}//addSorted
}//class