4.1.4—栈—Evaluate Reverse Polish Notation

描述

Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are +, -, *, /. Each operand may be an integer or another expression.

Some examples:

["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9

["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6

#include<iostream>
#include<string>
#include<stack>
#include<vector>
#include <sstream>
using namespace std;
bool Isoperate(string str)
{
if (str == "+" || str == "-" || str == "*" || str == "/")
return true;
else
return false;
}
int EvaluateReversePolish(vector<string> str)
{
stack<string> mystack;
for (int i = 0; i<str.size(); i++)
{
if (!Isoperate(str[i]))
mystack.push(str[i]);
else
{
int x = atoi(mystack.top().c_str());
mystack.pop();
int y = atoi(mystack.top().c_str());
mystack.pop();
if (str[i] == "+")
x = x + y;
else if (str[i] == "-")
x = x - y;
else if (str[i] == "*")
x = x*y;
else if (str[i] == "/")
x = y / x;
//===
string temp;
ostringstream oss;
oss << x;
temp = oss.str();
mystack.push(temp);
}
}
return atoi(mystack.top().c_str());
}
int main()
{

vector<string > str;
str.push_back("4");
str.push_back("13");
str.push_back("5");
str.push_back("/");
str.push_back("+");
int res = EvaluateReversePolish(str);
cout << res << endl;
}