leetcode.150. Evaluate Reverse Polish Notation

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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 result = 0;        int i;        stack<int> opd;         //存储操作数        int size = tokens.size();        for(i=0;i<size;i++)        {            if(tokens[i]=="*")            {                int rOpd = opd.top();   //右操作数                opd.pop();                int lOpd = opd.top();  //左操作数                opd.pop();                result = lOpd*rOpd;                opd.push(result);            }            else if(tokens[i]=="/")            {                int rOpd = opd.top();                opd.pop();                int lOpd = opd.top();                opd.pop();                result = lOpd/rOpd;                opd.push(result);            }            else if(tokens[i]=="+")            {                int rOpd = opd.top();                opd.pop();                int lOpd = opd.top();                opd.pop();                result = lOpd+rOpd;                opd.push(result);            }            else if(tokens[i]=="-")            {                int rOpd = opd.top();                opd.pop();                int lOpd = opd.top();                opd.pop();                result = lOpd-rOpd;                opd.push(result);            }            else            {                opd.push(atoi(tokens[i].c_str()));            }        }        return opd.top();    }};

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