leetcode - [2]Evaluate Reverse Polish Notation

Evaluate Reverse Polish Notation

Total Accepted: 24595 Total Submissions: 123794My Submissions

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

Have you been asked this question in an interview?
思路：栈的简单应用

#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <cstdlib>

using namespace std;

class Solution {
public:
int evalRPN(vector<string> &tokens) {
stack<int> s;
string str;
int a, b;

for (int i = 0; i < tokens.size(); i++) {
str = tokens[i];
if (str == "+" || str == "-" || str == "*" ||
a = s.top(); s.pop();
b = s.top(); s.pop();
switch(str[0]) {
case '+': s.push(b+a); break;
case '-': s.push(b-a); break;
case '*': s.push(b*a); break;
case '/': s.push(b/a); break;
}
}
else {
s.push(atoi(str.c_str()));
}
}
a = s.top();s.pop();
return a;
}
};

int main(int argc, char *argv[]) {
Solution* solution = new Solution();
vector<string> tokens;
tokens.push_back("2");
tokens.push_back("1");
tokens.push_back("+");
tokens.push_back("3");
tokens.push_back("*");

cout << solution->evalRPN(tokens) << endl;

vector<string> tokens2;
tokens2.push_back("4");
tokens2.push_back("13");
tokens2.push_back("5");
tokens2.push_back("/");
tokens2.push_back("+");
cout << solution->evalRPN(tokens2) << endl;
return 0;
}