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Evaluate Reverse Polish Notation

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

class Solution {public:    int evalRPN(vector<string> &tokens) {            int sum;    string operators="+-*/";    stack<int>sta;    for(int i=0;i<tokens.size();i++){        if(operators.find(tokens[i])==string::npos){            sta.push(atoi(tokens[i].c_str()));        }        else{            int a=sta.top();            sta.pop();            int b=sta.top();            sta.pop();            if(tokens[i]=="+"){                sta.push(a+b);            }            if(tokens[i]=="-"){                sta.push(b-a);            }            if(tokens[i]=="*"){                sta.push(a*b);            }            if(tokens[i]=="/"){                sta.push(b/a);            }        }                }    sum=sta.top();    return sum;    }};

 

Evaluate Reverse Polish Notation