[CC150][3.3] Imagine a (literal) stack of plates If the stack gets too high, it might topple Therefore, in real life, we would likely start a new stack when the previous stack exceeds some threshold Implement a data structure SetOfStacks that mimics this SetOfStacks should be composed of several stacks, and should create a new stack once the pre…

SetOfStacks.java

import java.util.Stack;
import java.util.ArrayList;

public class SetOfStacks<T> {
	private ArrayList<myStack> stacks;
	private int threshold;
	private int currIdx;
	
	private class myStack {
		Stack<T> stack;
		int N;
		
		public myStack() {
			stack = new Stack<T>();
			N = 0;
		}
		
		public void push(T item) {
			stack.add(item);
			N++;
		}
		
		public T pop() {
			if (N == 0) return null;
			N--;
			return stack.pop();
		}
 	}
	
	public SetOfStacks (int threshold) {
		stacks = new ArrayList<myStack>();
		stacks.add(new myStack());
		currIdx = 0;
		this.threshold = threshold;
	}
	
	public void push(T item) {
		myStack s = stacks.get(currIdx);
		if (s.N >= threshold) {
			currIdx++;
			stacks.add(new myStack());
			stacks.get(currIdx).push(item);
		}
		else stacks.get(currIdx).push(item);
	}
	
	public T pop() {
		while (stacks.get(currIdx).N == 0 && currIdx > 0) currIdx--;
		return stacks.get(currIdx).pop();
	}
	
	public T popAt(int index) {
		if (index  > currIdx) return null;
		return stacks.get(index).pop();
	}
	
	public String toString() {
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i <= currIdx; i++) {
			for (T each : stacks.get(i).stack) {
				sb.append(each.toString() + " ");
			}
			sb.append("\n");
		}
		return sb.toString();
	}
	
	
	public static void main(String[] args) {
		SetOfStacks<Integer> test = new SetOfStacks<Integer>(10);
		for (int i = 0; i < 60; i++)
			test.push(i);
		System.out.println(test.toString());
		
		for (int i = 0; i < 35; i++)
			test.pop();
		System.out.println(test.toString());
		
		for (int i = 0; i < 35; i++)
			test.push(i);
		System.out.println(test.toString());
		
		for (int i = 0; i < 7; i++)
			System.out.println(test.popAt(i));
		System.out.println(test.toString());
	}
}