[Java data structure] 3.1 sequential Stack

Stack

Definition:

Stack) is a linear table of Last in first out, LIFO). It must be deleted and inserted only at the end of the table.

The figure is as follows:

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Features:

I. Stack special linear table sequence table and linked list). It has some special requirements and restrictions on operations: the elements of the stack must be "post-in-first-out ".

3. the table at the end of the stack is called the top of the stack), and the corresponding header is called the bottom)

2. Stack operations can only be performed at the end of the linear table.

Implementation of the sequence Stack:

The time complexity of the push (), pop (), and peek () methods is O (1). When the stack capacity needs to be expanded, the time complexity of the push () method is O (n)

Package com. ds. stack; import java. util. Arrays; public class Stack <T> {// Java array implementation. You can use a java Generic Array. To use this function, use the private Object [] stack container provided by Java. // The default initial size of the stack is private final static int INIT_SIZE = 2. // The private int index of the top stack index; /*** default constructor ** the initial size of the Stack is default */public Stack () {this. stack = new Object [INIT_SIZE]; index =-1;}/*** constructor ** @ param initSize * Initial Stack size */public stack (int initSize) {if (initSize <0) throw new IllegalArgumentException (); this. stack = new Object [initSize]; index =-1 ;}/*** Stack exit Operation ** @ return top stack object */public synchronized T pop () {// return this. top =-1? Null :( T) this. element [this. top --]; if (! IsEmpty () {T temp = peek (); stack [index --] = null; return temp;} return null ;} /*** out stack operation ** @ return top stack object */public synchronized void push (T item) {if (isFull () {// if the stack is full, the created stack Object [] temp = stack; temp = new Object [2 * stack. length]; stack = Arrays. copyOf (temp, temp. length);} stack [++ index] = item;}/*** view stack top object ** @ return stack top object */public T peek () {// return this. top =-1? Null: (T) this. element [this. top]; if (! IsEmpty () {return (T) stack [index];} return null;}/*** check whether the stack is empty ** @ return true if the stack is empty, otherwise, false */public boolean isEmpty () {return index =-1;}/*** check whether the stack is full ** @ return returns true if the stack is full, otherwise, false */public boolean isFull () {return index = stack. length-1;} public static void main (String [] args) {Stack <Integer> stack = new Stack <Integer> (3); for (int I = 0; I <5; I ++) {stack. push (I);} System. out. println ("stack. top: "+ stack. peek ());}}

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