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
Solution: I implemented the algorithm provided in Reverse Polish Notation.
class Solution { public: bool isOperator(string token){ return token=="+" || token=="-" || token=="*" || token=="/"; } int cal(int lOperand, int rOperand, string op){ if(op=="+") return lOperand+rOperand; if(op=="-") return lOperand-rOperand; if(op=="*") return lOperand*rOperand; return lOperand/rOperand; } int evalRPN(vector<string> &tokens) { // IMPORTANT: Please reset any member data you declared, as // the same Solution instance will be reused for each test case. if(tokens.empty()) return INT_MIN; stack<int> s; for(size_t i=0; i<tokens.size(); ++i){ if(isOperator(tokens[i])){ if(s.size()>=2){ int rOperand = s.top(); s.pop(); int lOperand = s.top(); s.pop(); s.push(cal(lOperand, rOperand, tokens[i])); } else return INT_MIN; } else s.push(stoi(tokens[i])); } if(s.size()==1) return s.top(); return INT_MIN; } };