HDOJ1237

题目:http://acm.hdu.edu.cn/showproblem.php?pid=1237

题目描述:该题要求模拟实现计算器的加减乘除功能.

解题思路:运算符有优先级高低之分,借助栈将表达式(中缀表达式)转化为后缀表达式存于队列中,接着再次借助栈实现加减乘除功能.

1. #include <iostream>
2. #include <stack>
3. #include <queue>
4. #include <string>
5. using namespace std;
7. bool IsLowPriority(const string &s,const string &q)//the first parameter is in the stack to be compared
8. {
9.     if(s=="*" || s=="/")
10.         return true;
11.     if((s=="+" || s=="-") && (q=="+" || q=="-"))
12.         return true;
13.     return false;
14. }
16. double GetNum(const string &n)
17. {
18.     int len,cnt;
19.     double num;
20.     len=n.length();
21.     cnt=1;
22.     num=0;
23.     for(int i=len-1;i>=0;i--)
24.     {
25.         num += (n[i]-'0')*cnt;
26.         cnt *= 10;
27.     }
28.     return num;
29. }
31. int main()
32. {   
33.     int i;
34.     int len;
35.     double temp1,temp2,tempRes;
36.     string temp;
37.     char str[200];
38.     stack<string> s;
39.     stack<double> dStack;
40.     queue<string> q;
41.     while(gets(str))
42.     {       
43.         if(!strcmp(str,"0"))            
44.             break;
45.         while(!s.empty())
46.             s.pop();
47.         while(!q.empty())
48.             q.pop();
49.         while(!dStack.empty())
50.             dStack.pop();
51.         len=strlen(str);;
52.         temp="";
53.         /************infix to postfix conversion*******************/
54.         for(i=0;i<len;i++)
55.         {           
56.             if(str[i] != ' ')
57.             {
58.                 temp += str[i];             
59.             }
60.             else
61.             {
62.                 if(temp=="+" || temp=="-" || temp=="*" || temp=="/")
63.                 {
64.                     if(s.empty())
65.                         s.push(temp);
66.                     else
67.                     {
68.                         while(!s.empty() && IsLowPriority(s.top(),temp))
69.                         {
70.                             q.push(s.top());
71.                             s.pop();
72.                         }
73.                         s.push(temp);
74.                     }
75.                 }
76.                 else
77.                 {
78.                     q.push(temp);
79.                 }
80.                 temp="";                
81.             }           
82.         }
83.         if(temp != "")
84.             q.push(temp);
85.         while(!s.empty())
86.         {
87.             q.push(s.top());
88.             s.pop();
89.         }
90.         /********************compute**********************/
91.         while(!q.empty())
92.         {
93.             
94.             if(q.front()=="+" || q.front()=="-" || q.front()=="*" || q.front()=="/")
95.             {
96.                 temp2=dStack.top();
97.                 dStack.pop();
98.                 temp1=dStack.top();
99.                 dStack.pop();
100.                 if(q.front()=="+")
101.                     tempRes=temp1+temp2;
102.                 if(q.front()=="-")
103.                     tempRes=temp1-temp2;
104.                 if(q.front()=="*")
105.                     tempRes=temp1*temp2;
106.                 if(q.front()=="/")
107.                     tempRes=temp1/temp2;
108.                 dStack.push(tempRes);
109.                 q.pop();
110.             }
111.             else
112.             {
113.                 dStack.push(GetNum(q.front()));
114.                 q.pop();
115.             }
116.         }
117.         printf("%.2f/n",dStack.top());  
118.     }
120.     return 0;
121. }