leetcode——Evaluate Reverse Polish Notation 求算式值（AC）

標籤：string   字串數組   

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> myStack;        int first,second,merge;        for(int i=0; i<tokens.size(); i++)        {            if(tokens[i]=="+" || tokens[i]=="-" || tokens[i]=="*" || tokens[i]=="/")            {                first = myStack.top();                myStack.pop();                second = myStack.top();                myStack.pop();                if(tokens[i] == "+")                    merge = first + second;                else if(tokens[i] == "-")                    merge = second - first;                else if(tokens[i] == "*")                    merge = first * second;                else if(tokens[i] == "/")                    merge = second / first;            }            else            {                merge = atoi(tokens[i].c_str());            }            myStack.push(merge);        }        return myStack.top();    }};