标签：style blog http io color ar os sp for
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
逆波兰式，不用说，肯定考虑栈。
主要是题目所给的是字符串的数组，需要多次进行数字到字符串或者字符串到数字的转换，具体实现参考我的blog，整数转字符串，字符串转整数。
这里我采用的是c++标准库sstream来实现转换。
代码：
class Solution { private: bool isSymbol(string a){ return a=="+"||a=="-"||a=="*"||a=="/"; } int Evaluate(int a,int b,char c){ switch (c) { case ‘+‘: return a+b; break; case ‘-‘: return a-b; break; case ‘*‘: return a*b; break; case ‘/‘: return a/b; break; default: break; } } public: int evalRPN(vector<string> &tokens) { stack<string> container; for(int i=0;i<tokens.size();++i){ if(isSymbol(tokens[i])&&!container.empty()){ string temp2Str=container.top();container.pop(); string temp1Str=container.top();container.pop(); int temp2; int temp1; stringstream s; s<<temp2Str;s>>temp2; s.clear(); s<<temp1Str;s>>temp1; s.clear(); stringstream s2; int res=Evaluate(temp1,temp2,tokens[i][0]); s2<<res; string resStr=s2.str(); container.push(resStr); }else{ container.push(tokens[i]); } } s; int result=0; string reultStr=container.top(); s<<reultStr; s>>result; return result; } };
Evaluate Reverse Polish Notation
标签：style blog http io color ar os sp for
原文地址：http://www.cnblogs.com/fightformylife/p/4085810.html
