-
Notifications
You must be signed in to change notification settings - Fork 0
/
Prefix_expression_evaluation.java
90 lines (85 loc) · 2.97 KB
/
Prefix_expression_evaluation.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
import java.util.*;
/*
2008-37:Prefix expression evaluation
correct(1.00)
*/
public class Prefix_expression_evaluation {
public static void main(String[] argv){
Scanner scanner=new Scanner(System.in);
while(true){
Stack<Integer> stack=new Stack<Integer>();
boolean ck=true;
String line=scanner.nextLine();
if(line.equals("."))break;
char[] ch=new char[1025];
int ch_i=0;
for(int i=line.length()-1;i>=0;i--){
ch[ch_i]=line.charAt(i);
ch_i++;
}
for (int i=0;i<line.length();i++){
if(is_op(ch[i])){
if(stack.empty()){
ck=false;
break;
}else{
int num1= stack.pop();
if(stack.empty()){
ck=false;
break;
}
int num2= stack.pop();
switch (ch[i]){
case '+':
stack.push(num1+num2);
break;
case '-':
stack.push(num1-num2);
break;
case '*':
stack.push(num1*num2);
break;
case '/':
stack.push(num1/num2);
break;
case '%':
stack.push(num1%num2);
break;
}
}
} else if(is_num(ch[i])){
int num=Integer.parseInt(String.valueOf(ch[i]));
i++;
int w=10;
while(i<ch_i&&is_num(ch[i])){
num=num+w*Integer.parseInt(String.valueOf(ch[i]));
i++;
w=w*10;
}
stack.push(num);
i--;
}
}
if(ck){
if(stack.empty()){
System.out.println("illegal");
}else{
int ans= stack.pop();
if(!stack.empty()){
System.out.println("illegal");
}else{
System.out.println(ans);
}
}
}else{
System.out.println("illegal");
}
}
}
private static boolean is_num(char ch) {
return ('0'<=ch&&ch<='9');
}
private static boolean is_op(char ch) {
return (ch=='+' || ch=='-' || ch=='*' || ch=='/' || ch=='%');
}
}