标签：color i++ dia 操作符 amp cto public span turn
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
解题思路：已知后缀表达式，求值。用一个栈就可以实现。划重点。string到int的转化函数 stoi.判断是数字还是操作符更好的做法：isdigit(tokens[i].back())
class Solution { public: int calc(int &a, int &b, string op){ if(op=="+")return a+b; else if(op=="-")return a-b; else if(op=="*")return a*b; else return a/b; } int evalRPN(vector<string>& tokens) { stack<int>nums; int top1,top2; for(int i=0;i<tokens.size();i++){ if(tokens[i]=="+"||tokens[i]=="-"||tokens[i]=="*"||tokens[i]=="/"){ top2=nums.top(); nums.pop(); top1=nums.top(); nums.pop(); nums.push(calc(top1,top2,tokens[i])); } else{ nums.push(stoi(tokens[i])); } } return nums.top(); } };
150. Evaluate Reverse Polish Notation
标签：color i++ dia 操作符 amp cto public span turn
原文地址：http://www.cnblogs.com/tsunami-lj/p/7631565.html
