逆波兰表达式的java实现

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package com.yinlu.test1;

import java.util.ArrayList;
import java.util.List;

public class MyStack {
private List<String> l;
private int size;
public String top;

public MyStack() {
l = new ArrayList<String>();
size = 0;
top = null;
}

public int size() {
return size;
}

public void push(String s) {
l.add(s);
top = s;
size++;
}

public String pop() {
String s = l.get(size - 1);
l.remove(size - 1);
size--;
top = size == 0 ? null : l.get(size - 1);
return s;
}

}

第二个类：

package com.yinlu.test1;

import java.util.ArrayList;
import java.util.List;

public class solution {
private static MyStack ms1 = new MyStack();//生成逆波兰表达式的栈
private static MyStack ms2 = new MyStack();//运算栈

/**
* 将字符串转换为中序表达式
*/
public static List<String> zb(String s) {
List<String> ls = new ArrayList<String>();//存储中序表达式
int i = 0;
String str;
char c;
do {
if ((c = s.charAt(i)) < 48 || (c = s.charAt(i)) > 57) {
ls.add("" + c);
i++;
} else {
str = "";
while (i < s.length() && (c = s.charAt(i)) >= 48
&& (c = s.charAt(i)) <= 57) {
str += c;
i++;
}
ls.add(str);
}

} while (i < s.length());
return ls;
}
/**
* 将中序表达式转换为逆波兰表达式
*/
public static List<String> parse(List<String> ls) {
List<String> lss = new ArrayList<String>();
for (String ss : ls) {
if (ss.matches("\\d+")) {
lss.add(ss);
} else if (ss.equals("(")) {
ms1.push(ss);
} else if (ss.equals(")")) {

while (!ms1.top.equals("(")) {
lss.add(ms1.pop());
}
ms1.pop();
} else {
while (ms1.size() != 0 && getValue(ms1.top) >= getValue(ss)) {
lss.add(ms1.pop());
}
ms1.push(ss);
}
}
while (ms1.size() != 0) {
lss.add(ms1.pop());
}
return lss;
}
/**
* 对逆波兰表达式进行求值
*/
public static int jisuan(List<String> ls) {
for (String s : ls) {
if (s.matches("\\d+")) {
ms2.push(s);
} else {
int b = Integer.parseInt(ms2.pop());
int a = Integer.parseInt(ms2.pop());
if (s.equals("+")) {
a = a + b;
} else if (s.equals("-")) {
a = a - b;
} else if (s.equals("*")) {
a = a * b;
} else if (s.equals("\\")) {
a = a / b;
}
ms2.push("" + a);
}
}
return Integer.parseInt(ms2.pop());
}
/**
* 获取运算符优先级
* +,-为1 *,/为2 ()为0
*/
public static int getValue(String s) {
if (s.equals("+")) {
return 1;
} else if (s.equals("-")) {
return 1;
} else if (s.equals("*")) {
return 2;
} else if (s.equals("\\")) {
return 2;
}
return 0;
}

public static void main(String[] args) {
System.out.println(jisuan(parse(zb("0-8+((1+2)*4)-3+(2*7-2+2)"))));
}

}

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