逆波兰式转换与计算-优快云博客

下面的逆波兰式，不支持单目运算，以及｛｝、〔〕这两类的括号运算。对精度提供了设置，根据你输入的浮点数的小数位的位数来适应，返回和操作数相同位数的结果。由于写的匆忙，好存在很多缺陷。不足的地方希望能给出批评。

java 代码

1.stack.java
import java.util.LinkedList;
/**
* @author
*
* @2007-2-8
* @to-Email
*/
public class Stack {
private LinkedList stack = new LinkedList();
private int top = -1;
public void push(Object obj)
{
top++;
stack.addFirst(obj);
}
public Object pop()
{
Object obj = stack.getFirst();
top--;
stack.removeFirst();
return obj;
}
public Object top()
{
return stack.getFirst();
}
public boolean isEmpty()
{
if(top == -1 || stack.size() == 0)
return true;
else
return false;
}
}

2.将输入的表达式转换成逆波兰式

java 代码

package structure;
import java.util.ArrayList;
import java.util.List;
import java.util.StringTokenizer;
/**
* @author wei
*
* @2007-2-8
* @to-Email
*/
public class Calculate {
private List expression = new ArrayList();
private List operator = new ArrayList();
private Stack stack;
public Calculate(String input)
{
stack = new Stack();
StringTokenizer st = new StringTokenizer(input, "+-*/()", true);
while (st.hasMoreElements()) {
expression.add(st.nextToken());
}
}
public static boolean isOperator(String operator) {
if ("+".equals(operator) || "-".equals(operator)
|| "*".equals(operator) || "/".equals(operator)
|| "(".equals(operator) || ")".equals(operator))
return true;
else
return false;
}
public List doTrans()
{
for(int i = 0;i
{
String str = (String)expression.get(i);
if(str.equals("+") || str.equals("-"))
{
gotOper(str,1);
}else if(str.equals("*") || str.equals("/"))
{
gotOper(str,2);
}else if(str.equals("("))
{
stack.push("(");
}else if(str.equals(")"))
{
gotParen(str);
}else
{
operator.add(str);
}
}
while(!stack.isEmpty())
{
operator.add(stack.pop());
}
return operator;
}
public void gotOper(String opThis, int prec1) { // got operator from input
while (!stack.isEmpty()) {
String opTop = (String) stack.pop();
if (opTop.equals("(")) // if it's a '('
{
stack.push(opTop); // restore '('
break;
} else // it's an operator
{
int prec2; // precedence of new op
if (opTop.equals("+") || opTop.equals("-")) // find new op prec
prec2 = 1;
else
prec2 = 2;
if (prec2 < prec1) // if prec of new op less
{ // than prec of old
stack.push(opTop); // save newly-popped op
break;
} else
// prec of new not less
//output = output + opTop;
operator.add(opTop);// than prec of old
} // end else (it's an operator)
} // end while
stack.push(opThis); // push new operator
}
public void gotParen(String ch) { // got right paren from input
while (!stack.isEmpty()) {
String chx = (String)stack.pop();
if (chx.equals("(")) // if popped '('
break; // we're done
else
// output = output + chx; // output it
operator.add(chx);
}
}
public static void main(String[] args)
{
Calculate calculate = new Calculate("2+(4-3)*2");
List result = calculate.doTrans();
for(int i=0;i
{
System.out.println(result.get(i));
}
}
}

3.后序表达式计算

java 代码

package structure;
import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
/**
* @author
*
* @2007-2-8
* @to-Email
*/
public class PostControl {
private List operator = new ArrayList();
private Stack stack = new Stack();
public PostControl(List list)
{
operator = list;
}
public String doParse()
{
BigDecimal z = new BigDecimal("0.00");
for(int i= 0;i
{
String str = (String)operator.get(i);
if(!isOperator(str))
{ stack.push(str);}
else
{
BigDecimal y = new BigDecimal((String)stack.pop());
BigDecimal x =new BigDecimal((String)stack.pop());
if(str.equals("+"))
{
z = x.add(y);
}else if(str.equals("-"))
{
z= x.subtract(y);
}else if(str.equals("*"))
{
z = x.multiply(y);
}else if(str.equals("/"))
{
z = x.divide(y);
}else
{
z= new BigDecimal("0.00");
}
stack.push(String.valueOf(z));
}
}
return (String)stack.pop();
}
public static boolean isOperator(String operator) {
if ("+".equals(operator) || "-".equals(operator)
|| "*".equals(operator) || "/".equals(operator)
|| "(".equals(operator) || ")".equals(operator))
return true;
else
return false;
}
public static void main(String[] args)
{
Calculate calculate = new Calculate("2+((4.5-3)*2+3)*2");
List result = calculate.doTrans();
PostControl p = new PostControl(result);
System.out.println(p.doParse());
}
}

逆波兰式计算