课下选作Main dc
一.中后缀定义：
中缀表达式：我们平时写的数学表达式一般为中缀表达式，如“5+2(3(3-12+1))”，直接拿中缀表达式直接让计算机计算表达式的结果并不能做到。
后缀表达式：把中缀表达表达式“5+2(3(3-12+1))”转化“523312-1+**+”这样的形式，就是后缀表达式。
二.原理
堆栈的使用
三.代码以及运行截图
import java.util.Stack;
/j计算后缀表达式
20175131王泽龙
/
public class Main {
static Stack
public static Float getv(char op, Float f1, Float f2){
if(op == '+') return f2 + f1;
else if(op == '-') return f2 - f1;
else if(op == '
else if(op == '/') return f2 / f1;
else return Float.valueOf(-0); }
/**
* calculate the value of the reverse Polish expression
* @param rp - reverse Polish expression
* @return - result of the expression
/
public static float calrp(String rp){
Stack
char[] arr = rp.toCharArray();
int len = arr.length;
for(int i = 0; i < len; i++){
Character ch = arr[i];
// if is operand, push to the stack
if(ch >= '0' && ch <= '9') v.push(Float.valueOf(ch - '0'));
// if is operator, calculate the result
// with top 2 operands in the stack,
// push the result into the stack
else v.push(getv(ch, v.pop(), v.pop()));
}
return v.pop();
}
/
* from infix to postfix
* @param s - String in the form of infix
* @return String in the form of postfix
/
public static String getrp(String s){
char[] arr = s.toCharArray();
int len = arr.length;
String out = "";
for(int i = 0; i < len; i++){
char ch = arr[i];
if(ch == ' ') continue;
// if is operand, add to
// the output stream directly
if(ch >= '0' && ch <= '9') {
out+=ch;
continue;
}
//if is '(', push to the stack directly
if(ch == '(') op.push(ch);
//if is '+' or '-', pop the operator
// from the stack until '(' and add to
// the output stream
//push the operator to the stack
if(ch == '+' || ch == '-'){
while(!op.empty() && (op.peek() != '('))
out+=op.pop();
op.push(ch);
continue;
}
//if is '' or '/', pop the operator stack and
// add to the output stream
// until lower priority or '('
//push the operator to the stack
if(ch == '' || ch == '/'){
while(!op.empty() && (op.peek() == '' || op.peek() == '/'))
out+=op.pop();
op.push(ch);
continue;
}
//if is ')' pop the operator stack and
// add to the output stream until '(',
// pop '('
if(ch == ')'){
while(!op.empty() && op.peek() != '(')
out += op.pop();
op.pop();
continue;
}
}
while(!op.empty()) out += op.pop();
return out;
}
public static void main(String[] args){
//constraint: the operand should be
// equal or greater than 0
// but equal or less than 9
String exp = "5+5(3(2-1))";
System.out.println(calrp(getrp(exp)));
}
}
我做的比较简单，计算的表达式固定：5+5(3(2-1))
