package Question3_3;

import java.util.ArrayList;

public class SetOfStacks {

ArrayList<Stack> stacks = new ArrayList<Stack>();

public int capacity;

public SetOfStacks(int capacity) {

this.capacity = capacity;

}

public Stack getLastStack() {

if (stacks.size() == 0) {

return null;

}

return stacks.get(stacks.size() - 1);

}

public void push(int v) {

Stack last = getLastStack();

if (last != null && !last.isFull()) { // add to last

last.push(v);

} else { // must create new stack

Stack stack = new Stack(capacity);

stack.push(v);

stacks.add(stack);

}

}

public int pop() {

Stack last = getLastStack();

int v = last.pop();

if (last.size == 0) {

stacks.remove(stacks.size() - 1);

}

return v;

}

public int popAt(int index) {

return leftShift(index, true);

}

public int leftShift(int index, boolean removeTop) {

Stack stack = stacks.get(index);

int removed_item;

if (removeTop) removed_item = stack.pop();

else removed_item = stack.removeBottom();

if (stack.isEmpty()) {

stacks.remove(index);

} else if (stacks.size() > index + 1) {

int v = leftShift(index + 1, false);

stack.push(v);

}

return removed_item;

}

public boolean isEmpty() {

Stack last = getLastStack();

return last == null || last.isEmpty();

}

}