4.1栈
栈的定义：又称堆栈，它是运算受限的线性表，其限制是仅允许在表的一段进行插入和删除操作，不允许在其他任何位置进行插入，查找，删除等操作。
栈的接口Stack：
1 package com.datastructure.chapter04.interfaces; 2 3 import com.datastructure.chapter04.Exception.StackEmptyException; 4 5 /** 6 * @ClassName: Stack 7 * @Description: 栈接口 8 * @author 9 * @date 2018年3月16日 下午8:52:24 10 * 11 */ 12 public interface Stack { 13 14 //返回堆栈的大小 15 public int getSize(); 16 17 //判断堆栈是否为空 18 public boolean isEmpty(); 19 20 //数据元素e入栈 21 public void push(Object e); 22 23 //栈顶元素出栈 24 public Object pop() throws StackEmptyException; 25 26 //取栈顶元素 27 public Object peek() throws StackEmptyException; 28 29 30 }
空栈抛出的异常类：
1 package com.datastructure.chapter04.Exception; 2 3 @SuppressWarnings("serial") 4 public class StackEmptyException extends RuntimeException { 5 6 public StackEmptyException(String err) { 7 super(err); 8 } 9 10 }
4.1.2 Stack的顺序存储实现
1 package com.datastructure.chapter04.interfaces; 2 3 import com.datastructure.chapter04.Exception.StackEmptyException; 4 5 /** 6 * @ClassName: StackArray 7 * @Description: 栈的顺序存储实现 8 * @author 9 * @date 2018年3月16日 下午9:05:52 10 * 11 */ 12 public class StackArray implements Stack { 13 14 private final int LEN = 8;//数组的默认大小 15 private Object[] elements;//数据元素数组 16 private int top;//栈顶指针 17 18 19 public StackArray(){ 20 top = -1; 21 elements = new Object[LEN]; 22 } 23 24 25 /* (非 Javadoc) 26 * <p>Title: getSize</p> 27 * <p>Description: 返回堆栈的大小</p> 28 * @return 29 * @see com.datastructure.chapter04.interfaces.Stack#getSize() 30 */ 31 @Override 32 public int getSize() { 33 return top+1; 34 } 35 36 /* (非 Javadoc) 37 * <p>Title: isEmpty</p> 38 * <p>Description: 判断堆栈的大小</p> 39 * @return 40 * @see com.datastructure.chapter04.interfaces.Stack#isEmpty() 41 */ 42 @Override 43 public boolean isEmpty() { 44 45 return top<0; 46 } 47 48 /* (非 Javadoc) 49 * <p>Title: push</p> 50 * <p>Description: 数据元素e入栈</p> 51 * @param e 52 * @see com.datastructure.chapter04.interfaces.Stack#push(java.lang.Object) 53 */ 54 @Override 55 public void push(Object e) { 56 if(getSize()>=elements.length) expandSpace(); 57 elements[++top] = e; 58 } 59 60 /** 61 * @Title: expandSpace 62 * @Description: 对数组进行扩容 63 * @param 64 * @return void 65 * @throws 66 */ 67 private void expandSpace() { 68 Object[] a = new Object[elements.length*2]; 69 for (int i = 0; i < elements.length; i++) 70 a[i] = elements[i]; 71 elements = a; 72 } 73 74 75 /* (非 Javadoc) 76 * <p>Title: pop</p> 77 * <p>Description: 栈顶元素出栈</p> 78 * @return 79 * @throws StackEmptyException 80 * @see com.datastructure.chapter04.interfaces.Stack#pop() 81 */ 82 @Override 83 public Object pop() throws StackEmptyException { 84 if(getSize()<1) 85 throw new StackEmptyException("错误，堆栈为空。"); 86 Object obj = elements[top]; 87 elements[top--]= null; 88 return obj; 89 } 90 91 /* (非 Javadoc) 92 * <p>Title: peek</p> 93 * <p>Description: 取栈顶元素</p> 94 * @return 95 * @throws StackEmptyException 96 * @see com.datastructure.chapter04.interfaces.Stack#peek() 97 */ 98 @Override 99 public Object peek() throws StackEmptyException { 100 if(getSize()<1) 101 throw new StackEmptyException("错误，堆栈为空。"); 102 return elements[top]; 103 } 104 105 106 }
push、pop、peek运行时间都是O(1).
4.1.3 Stack的链式存储实现
1 package com.datastructure.chapter04.impl; 2 3 import com.datastructure.chapter04.Exception.StackEmptyException; 4 import com.datastructure.chapter04.interfaces.Stack; 5 6 public class StackSLinked implements Stack { 7 8 private SLNode top;//链表首结点引用 9 10 private int size; //栈的大小 11 12 public StackSLinked() { 13 top = null; 14 size = 0; 15 } 16 17 18 /* (非 Javadoc) 19 * <p>Title: getSize</p> 20 * <p>Description: 返回堆栈的大小</p> 21 * @return 22 * @see com.datastructure.chapter04.interfaces.Stack#getSize() 23 */ 24 @Override 25 public int getSize() { 26 return size; 27 } 28 29 /* (非 Javadoc) 30 * <p>Title: isEmpty</p> 31 * <p>Description: 判断堆栈是否为空 </p> 32 * @return 33 * @see com.datastructure.chapter04.interfaces.Stack#isEmpty() 34 */ 35 @Override 36 public boolean isEmpty() { 37 38 return size == 0; 39 } 40 41 /* (非 Javadoc) 42 * <p>Title: push</p> 43 * <p>Description: 数据元素进栈</p> 44 * @param e 45 * @see com.datastructure.chapter04.interfaces.Stack#push(java.lang.Object) 46 */ 47 @Override 48 public void push(Object e) { 49 SLNode q = new SLNode(e, top); 50 top = q; 51 size++; 52 } 53 54 /* (非 Javadoc) 55 * <p>Title: pop</p> 56 * <p>Description: 栈顶出栈</p> 57 * @return 58 * @throws StackEmptyException 59 * @see com.datastructure.chapter04.interfaces.Stack#pop() 60 */ 61 @Override 62 public Object pop() throws StackEmptyException { 63 if(size<1) 64 throw new StackEmptyException("错误，堆栈为空"); 65 Object obj = top.getData(); 66 top = top.getNext(); 67 return obj; 68 } 69 70 /* (非 Javadoc) 71 * <p>Title: peek</p> 72 * <p>Description: 取栈顶元素</p> 73 * @return 74 * @throws StackEmptyException 75 * @see com.datastructure.chapter04.interfaces.Stack#peek() 76 */ 77 @Override 78 public Object peek() throws StackEmptyException { 79 80 if(size<1) 81 throw new StackEmptyException("错误，堆栈为空"); 82 return top.getData(); 83 } 84 85 }
所有的操作都在O(1)时间内完成