import java.util.ArrayList
import java.util.Stack
/**
*
* @author yhh
*
*/
public class Calculate {
/**
* 将字符串转化成List
* @param str
* @return
*/
public ArrayList<String>getStringList(String str){
ArrayList<String>result = new ArrayList<String>()
String num = ""
for (int i = 0i <str.length()i++) {
if(Character.isDigit(str.charAt(i))){
num = num + str.charAt(i)
}else{
if(num != ""){
result.add(num)
}
result.add(str.charAt(i) + "")
num = ""
}
}
if(num != ""){
result.add(num)
}
return result
}
/**
* 将中缀表达式转化为后缀表达式
* @param inOrderList
* @return
*/
public ArrayList<String>getPostOrder(ArrayList<String>inOrderList){
ArrayList<String>result = new ArrayList<String>()
Stack<String>stack = new Stack<String>()
for (int i = 0i <inOrderList.size()i++) {
if(Character.isDigit(inOrderList.get(i).charAt(0))){
result.add(inOrderList.get(i))
}else{
switch (inOrderList.get(i).charAt(0)) {
case '(':
stack.push(inOrderList.get(i))
break
case ')':
while (!stack.peek().equals("(")) {
result.add(stack.pop())
}
stack.pop()
break
default:
while (!stack.isEmpty() &&compare(stack.peek(), inOrderList.get(i))){
result.add(stack.pop())
}
stack.push(inOrderList.get(i))
break
}
}
}
while(!stack.isEmpty()){
result.add(stack.pop())
}
return result
}
/**
* 计算后缀表达式
* @param postOrder
* @return
*/
public Integer calculate(ArrayList<String>postOrder){
Stack stack = new Stack()
for (int i = 0i <postOrder.size()i++) {
if(Character.isDigit(postOrder.get(i).charAt(0))){
stack.push(Integer.parseInt(postOrder.get(i)))
}else{
Integer back = (Integer)stack.pop()
Integer front = (Integer)stack.pop()
Integer res = 0
switch (postOrder.get(i).charAt(0)) {
case '+':
res = front + back
break
case '-':
res = front - back
break
case '*':
res = front * back
break
case '/':
res = front / back
break
}
stack.push(res)
}
}
return (Integer)stack.pop()
}
/**
* 比较运算符等级
* @param peek
* @param cur
* @return
*/
public static boolean compare(String peek, String cur){
if("*".equals(peek) &&("/".equals(cur) || "*".equals(cur) ||"+".equals(cur) ||"-".equals(cur))){
return true
}else if("/".equals(peek) &&("/".equals(cur) || "*".equals(cur) ||"+".equals(cur) ||"-".equals(cur))){
return true
}else if("+".equals(peek) &&("+".equals(cur) || "-".equals(cur))){
return true
}else if("-".equals(peek) &&("+".equals(cur) || "-".equals(cur))){
return true
}
return false
}
public static void main(String[] args) {
Calculate calculate = new Calculate()
String s = "12+(23*3-56+7)*(2+90)/2"
ArrayList result = calculate.getStringList(s) //String转换为List
result = calculate.getPostOrder(result) //中缀变后缀
int i = calculate.calculate(result) //计算
System.out.println(i)
}
}
