#include <iostream>
#include <vector>
#include <algorithm>
#include <stack>
#include <queue>
#include <string>
#include <map>
using namespace std;
struct Node{
int num;
char op;
int flag;//flag指示是数字还是符号,为0表示数字为1表示符号
};
stack<Node> t;//栈：用于转后缀时的符号栈和计算值时的数字栈
queue<Node> q;//记录后缀表达式
map<char,int> m;//用于指示操作符的优先级
Node node;
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
m['+'] = 1; m['-'] = 1;
m['*'] = 2; m['/'] = 2;
int i,j,n,l,r;
cin>>n;
string str;
char op;
for(i = 0 ;i < n ;i++)
{
while(!t.empty()) t.pop();
while(!q.empty()) q.pop();
cin>>str;
for(j = 0 ;j < (int)str.length() ; )
{
if(str[j]>='0'&&str[j]<='9')
{
node.flag = 0;
node.num = str[j++] - '0';
while(str[j]>='0'&&str[j]<='9')
{
node.num = node.num*10+str[j] - '0';
j++;
}
q.push(node);
}else{
node.flag = 1;
node.op = str[j];
if(str[j] == '(')
{
t.push(node);
}else if(str[j] == ')'){
while(t.top().op!='(')
{
q.push(t.top());
t.pop();
}
t.pop();
}else{
while(!t.empty()&&m[str[j]]<=m[t.top().op])
{
q.push(t.top());
t.pop();
}
t.push(node);
}
j++;
}
}
while(!t.empty())
{
q.push(t.top());
t.pop();
}
//此时的q已经存好了后缀表达式
while(!q.empty())
{
if(q.front().flag == 0)
{
t.push(q.front());
q.pop();
}else if(q.front().flag == 1){
r = t.top().num;
t.pop();
l = t.top().num;
t.pop();
op = q.front().op;
if(op == '+') node.num = l+r;
else if(op == '-') node.num = l-r;
else if(op == '*') node.num = l*r;
else if(op == '/') node.num = l/r;
t.push(node);
q.pop();
}
}
cout<<t.top().num<<endl;
}
return 0;
}
可用此段代码查看后缀表达式：
while(!q.empty())
{
if(q.front().flag == 0)
cout<<q.front().num;
else
cout<<q.front().op;
q.pop();
}