首页 > 代码库 > Evaluate Reverse Polish Notation

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) {        stack<int> nums;        int num = tokens.size();        int i=0;        if(num == 1) return tonum(tokens[0]);        while(i<num){            while(i<num && !isop(tokens[i])){                int tmp = tonum(tokens[i]);                nums.push(tmp);                i++;            }            int op2 = nums.top();            nums.pop();            int op1 = nums.top();            nums.pop();            if(tokens[i] == "+"){                nums.push(op1+op2);            }            else if(tokens[i] == "*"){                nums.push(op1 * op2);            }            else if(tokens[i] == "-"){                nums.push(op1 - op2);            }            else if(tokens[i] == "/"){                nums.push(op1 / op2);            }            i++;        }        return nums.top();    }    int tonum(string s){        int num;        stringstream ss(s);        ss >> num;        return num;    }    bool isop(string str){        if(str.length() > 1) return false;        if(str == "+") return true;        if(str == "*") return true;        if(str == "-") return true;        if(str == "/") return true;    }};

 

Evaluate Reverse Polish Notation