中缀表达式和后缀表达式的转换
import java.util.ArrayList;
import java.util.List;
import java.util.Stack;
public class Test1 {
public static void main(String[] args) {
String ss = "1+((2+3)*4)-5";
List<String> ls = infixExp(ss);
System.out.println(ls);
List<String> sufL = sufList(ls);
System.out.println(sufL);
System.out.print(cal(sufL));
}
public static List<String> sufList(List<String> lls){
Stack<String> stack = new Stack<String>();
List<String> suf = new ArrayList<String>();
for(String s:lls) {
if(s.matches("\\d+")) {
suf.add(s);
}else if(s.equals("(")) {
stack.add(s);
}else if(s.equals(")")) {
while(true) {
if(!stack.peek().equals("(")) {
suf.add(stack.pop());
}else {
break;
}
}
stack.pop();
}else {
while(stack.size() != 0 && Operation.getValue(stack.peek()) >= Operation.getValue(s)) {
suf.add(stack.pop());
}
stack.push(s);
}
}
while(true) {
if(stack.size() == 0) {
break;
}
suf.add(stack.pop());
}
return suf;
}
public static List<String> infixExp(String s){
List<String> ls = new ArrayList<String>();
String str = "";
char c = ' ';
int index = 0;
while(true) {
if(index >= s.length()) {
break;
}
c = s.charAt(index);
if(c < 48 || c > 57) {
ls.add(""+c);
}else {
if(index == s.length()-1) {
str+=c;
ls.add(str);
}else {
if(s.charAt(index+1) >= 48 && s.charAt(index+1) <= 57) {
str+=c;
}else{
str+=c;
ls.add(str);
str="";
}
}
}
index++;
}
return ls;
}
public static int cal(List<String> ls) {
Stack<String> stack = new Stack<String>();
int index = 0;
while(true) {
if(index >= ls.size()) {
break;
}
String s = ls.get(index);
if(s.matches("\\d+")) {
stack.push(s);
}else {
int num2 = Integer.parseInt(stack.pop());
int num1 = Integer.parseInt(stack.pop());
int res = 0;
if(s.equals("+")) {
res = num1 + num2;
}
else if(s.equals("-")) {
res = num1 - num2;
}
else if(s.equals("*")) {
res = num1 * num2;
}
else if(s.equals("/")) {
res = num1 / num2;
}else {
System.out.println("符号有问题!");
}
stack.push(res+"");
}
index++;
}
return Integer.parseInt(stack.pop());
}
}
class Operation {
private static int ADD = 1;
private static int SUB = 1;
private static int MUL = 2;
private static int DIV = 2;
public static int getValue(String string) {
int result = 0;
switch(string) {
case "+":
result = ADD;
return result;
case "-":
result = SUB;
return result;
case "*":
result = MUL;
return result;
case "/":
result = DIV;
return result;
default:
break;
}
return result;
}
}