栈和队列——用数组实现栈和队列

用数组结构实现大小固定的栈 （较简单）

栈是先进后出

public class ArrayStack{
        private int size;
        private int [] arraySta;
        private int index = 0;

        public ArrayStack(int size) {
            if(size < 0){
                throw new IllegalArgumentException( "size must be positive" );
            }
            this.size = size;
            this.arraySta = new int[this.size];
        }

        public void push(int num){
            if(index == size) {
                throw new ArrayIndexOutOfBoundsException( "this stack is full" );
            }
            arraySta[index++] = num;
        }

        public int pop(){
            if(index == 0){
                throw new ArrayIndexOutOfBoundsException( "this stack is empty" );
            }
            return arraySta[--index];
        }

        public int peek(){
            if(index == 0){
                throw new ArrayIndexOutOfBoundsException("this stack is empty");
            }
            return arraySta[index - 1];
        }
    }

　　

用数组结构实现大小固定的队列 （较复杂）

队列是先进先出

注意：不要试图使用head和tail两个指针之间的关系进行判断，很复杂

head和tail分别从头开始，触底就从头开始，

只利用它们与size之间的关系，size==0时，出队列poll()抛出异常，size==array.length时，入队列offer()抛出异常

以及与数组的长度head==array.length时，tail==array.length时，从头开始

 

//数组实现队列  先进先出 head指向出元素端，tail直线进元素端
    public class ArrayQueue{
        private int size;
        private int[] arrayQue;
        private int head;
        private int tail;

        public ArrayQueue(int size) {
            this.arrayQue = new int[size];
            this.head = 0;
            this.tail = 0;
            this.size = 0;
        }

        //向队列中添加元素
        public void offer(int num){
            if(size == arrayQue.length){
                throw new ArrayIndexOutOfBoundsException("queue is full");
            }
            arrayQue[tail++] = num;
            size++;
            if(tail == arrayQue.length) tail = 0;
        }

        //从队列中弹出元素
        public int poll(){
            if(size == 0){
                throw new ArrayIndexOutOfBoundsException("queue is empty");
            }
            int num = arrayQue[head++];
            size--;
            if(head == arrayQue.length) head = 0;
            return num;
        }

        //获取队列的头部元素
        public int peek(){
            if(size == 0){
                throw new ArrayIndexOutOfBoundsException("queue is empty");
            }
            return arrayQue[head];
        }
    }