标签：des style blog java color os
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 structureSetOf Stacks that mimics this. SetOf Stacks should be composed of several stacks and should create a new stack once the previous one exceeds capacity. SetOfStacks.push() and SetOfStacks.pop() should be have identically to a single stack(that is,pop() should return the same values as it would if there were just a single stack).
FOLLOW UP
Implement a function popAt(int index) which performs a pop operation on a specific sub-stack.
Using arraylist could easily implement stacks, and use another arraylist to manage these stacks, when the current stack is full, add a new one, when the current is empty, remove it from the list. In terms of popAt(), I assume that after pop the top from the specific stack, the hole would not be filled in the following push process. We could ask interviewer to clarify this problem. Besides, I assume the data type to be integer, we could use generalization to implement the class.
/*Use arraylist to implement stacks and another arraylist to store these stacks, assume the elements are integer to ease the discussion. I assume that after a popAt() call, the newly pushed elements should still see the entire stack as a single stack.*/ import java.util.*; public class SetofStacks { ArrayList<ArrayList<Integer>> sets; int stackSize; int stackNum = -1; public SetofStacks(int size) { sets = new ArrayList<ArrayList<Integer>>(); stackSize = size; } public void push(int key) { //If there is no stack yet or the current stack is full, create a new one if(stackNum == -1 || sets.get(stackNum).size()+1 > stackSize) { sets.add(new ArrayList<Integer>()); stackNum++; } sets.get(stackNum).add(key); } public int pop() throws Exception { if(stackNum == -1) { throw new Exception("No Elements"); } int top = sets.get(stackNum).size(); int key = sets.get(stackNum).get(top-1); sets.get(stackNum).remove(top-1); //If a stack is empty, remove it from the list if(sets.get(stackNum).size() == 0) { sets.remove(stackNum); stackNum--; } return key; } public int popAt(int index) throws Exception{ if(stackNum < index) { throw new Exception("No Such Stack"); } int top = sets.get(index).size(); int key = sets.get(index).get(top-1); sets.get(index).remove(top-1); return key; } public static void main(String[] args) { SetofStacks ss = new SetofStacks(2); try { ss.push(1); ss.push(2); ss.push(3); System.out.println(ss.pop() + " " + ss.pop() + " " +ss.pop()); ss.push(1); ss.push(2); ss.push(3); ss.push(4); System.out.println(ss.popAt(0) + " " + ss.popAt(1)); ss.push(5); ss.push(6); System.out.println(ss.pop() + " " + ss.pop() + " " +ss.pop()); } catch(Exception e) { System.out.println(e.toString()); } } }
标签：des style blog java color os
原文地址：http://www.cnblogs.com/pyemma/p/3835206.html
