1. 总体思路,定义数据栈存放数据, 只要遇到运算符就出栈两个数作加减乘除处理.spa
class Solution { public: int evalRPN(vector<string>& tokens) { stack<int> st; for(int i=0;i<tokens.size();i++) { if(tokens[i]!="+" && tokens[i]!="-" && tokens[i]!="*" && tokens[i]!="/") { int num = stoi(tokens[i]); st.push(num); } else { int second = st.top(); st.pop(); int first = st.top(); st.pop(); int all = 0; if(tokens[i]=="+") all = first+second; if(tokens[i]=="-") all = first-second; if(tokens[i]=="*") all = first*second; if(tokens[i]=="/") all = first/second; st.push(all); } } return st.top(); } };