栈

 

栈：

 

数组实现TOP指向下一个位置

 

 

栈 计算后缀表达式

 

从左到右扫描表达式，依次标识出每个符号（操作符或操作数）

如果是操作数压入栈中。如果是操作符则从栈中弹出两个元素并把该

操作符应用在这连个元素上，然后操作结果压入栈中。

 

/** * Evaluates the specified postfix expression. If an operand is * encountered, it is pushed onto the stack. If an operator is * encountered, two operands are popped, the operation is * evaluated, and the result is pushed onto the stack. * @param expr String representation of a postfix expression * @return int value of the given expression */ public int evaluate (String expr) { int op1, op2, result = 0; String token; StringTokenizer tokenizer = new StringTokenizer (expr); while (tokenizer.hasMoreTokens()) { token = tokenizer.nextToken(); if (isOperator(token)) { op2 = (stack.pop()).intValue(); op1 = (stack.pop()).intValue(); result = evalSingleOp (token.charAt(0), op1, op2); stack.push (new Integer(result)); } else stack.push (new Integer(Integer.parseInt(token))); } return result; }  

 

栈: 链式实现

 

用一个特别的LinerNode<T>

 

/** * @author Lewis and Chase * * Represents a node in a linked list. */ package jss2; public class LinearNode<T> { /** reference to next node in list */ private LinearNode<T> next; /** element stored at this node */ private T element; /** * Creates an empty node. */ public LinearNode() { next = null; element = null; } /** * Creates a node storing the specified element. * @param elem element to be stored */ public LinearNode (T elem) { next = null; element = elem; } /** * Returns the node that follows this one. * @return LinearNode<T> reference to next node */ public LinearNode<T> getNext() { return next; } /** * Sets the node that follows this one. * @param node node to follow this one */ public void setNext (LinearNode<T> node) { next = node; } /** * Returns the element stored in this node. * @return T element stored at this node */ public T getElement() { return element; } /** * Sets the element stored in this node. * @param elem element to be stored at this node */ public void setElement (T elem) { element = elem; } }  

 

push操作：

/** * Adds the specified element to the top of this stack. * @param element element to be pushed on stack */ public void push (T element) { LinearNode<T> temp = new LinearNode<T> (element); temp.setNext(top); top = temp; count++; }  

 

pop操作

/** * Removes the element at the top of this stack and returns a * reference to it. Throws an EmptyCollectionException if the stack * is empty. * @return T element from top of stack * @throws EmptyCollectionException on pop from empty stack */ public T pop() throws EmptyCollectionException { if (isEmpty()) throw new EmptyCollectionException("Stack"); T result = top.getElement(); top = top.getNext(); count--; return result; } 

 

使用栈来穿越迷宫

/** * Attempts to iteratively traverse the maze. It inserts special * characters indicating locations that have been tried and that * eventually become part of the solution. This method uses a * stack to keep track of the possible moves that could be made. * @return boolean returns true if the maze is successfully traversed */ public boolean traverse () { boolean done = false; Position pos = new Position(); Object dispose; StackADT<Position> stack = new LinkedStack<Position>(); stack.push(pos); while (!(done)) { pos = stack.pop(); grid[pos.getx()][pos.gety()] = TRIED; // this cell has been tried if (pos.getx() == grid.length-1 && pos.gety() == grid[0].length-1) done = true; // the maze is solved else { stack = push_new_pos(pos.getx(),pos.gety() - 1, stack); stack = push_new_pos(pos.getx(),pos.gety() + 1, stack); stack = push_new_pos(pos.getx() - 1,pos.gety(), stack); stack = push_new_pos(pos.getx() + 1,pos.gety(), stack); } } return done; } 

 

 

tips:

 

 

1.通常均给出其无参数构造函数.

 

 

2.数据结构在定义时用到泛型，在具体应用的时候给出泛型的具体。

 

 

3.以上穿越迷宫两种结束while(!done)循环一种是success找到通路.

另一种是弹出下一个可选位置时间报空。抛出异常，程序中止.

 

 

4.检查是否valid

不超出grid范围并且为通路即为1。。

 

 

5.以count为计数器，记录当前结构中的element数，isEmpty()和size()中直接用

 

6.要返回某值时 定义 T result将其返回。