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NiBoLan.java
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100 lines (97 loc) · 3.01 KB
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package basic.QueueAndStack;
import java.util.Stack;
public class NiBoLan {
public static void main(String[] args) {
String str=new NiBoLan().niBoLan("2-(2-1)+3-(2-10)");
System.out.println(new NiBoLan().calNiBoLan(str));
}
//后缀表达值计算值
public int calNiBoLan(String str) {
Stack<Integer> numStack=new Stack<>();
int num=0;
for (int i=0;i<str.length();i++) {
char c=str.charAt(i);
if(Character.isDigit(c)) {
num=c-'0';
while (i+1<str.length() && str.charAt(i+1)!=' ') {
num=10*num+(str.charAt(i+1)-'0');
i++;
}
numStack.push(num);
i++;//略过空格
}else {
int b=numStack.pop();
int a=numStack.pop();
int tmp;
switch (c) {
case '*':
tmp=a*b;
break;
case '/':
tmp=a/b;
break;
case '+':
tmp=a+b;
break;
case '-':
tmp=a-b;
break;
default:
tmp=0;
break;
}
numStack.push(tmp);
}
}
return numStack.pop();
}
/**
* 中缀表达式转后缀表达式
* @param str
* @return
*/
public String niBoLan(String str) {
StringBuilder sb=new StringBuilder();
Stack<Character> opStack=new Stack<>();
for (int i=0;i<str.length();i++) {
char c=str.charAt(i);
if(c==' ') continue;
if(Character.isDigit(c)) {
sb.append(c);
while (i+1<str.length() && Character.isDigit(str.charAt(i+1))) {
sb.append(str.charAt(i+1));
i++;
}
//数字之间以空格分隔
sb.append(' ');
}else {
char tmp;
if(c=='(') opStack.push(c);
if(c==')') while ((tmp=opStack.pop())!='(') sb.append(tmp);
if(c=='*' || c=='/' || c=='+' || c=='-') {
//扫描到的运算符优先级大于栈顶，直接压栈。
while (!opStack.isEmpty() && getPriority(c)<=getPriority((opStack.peek()))) {
sb.append(opStack.pop());
}
opStack.push(c);
}
}
}
while (!opStack.isEmpty()) {
sb.append(opStack.pop());
}
return sb.toString();
}
int getPriority(char op) {
switch (op) {
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
default:
return 0;
}
}
}