c++编程学习

LeetCode OJ：
Evaluate 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

#include<iostream>
#include<vector>
#include<string>
#include<stack>
#include<stdlib.h>
#include<ctype.h>
using namespace std;
class Solution
{
public:
	int evalRPN( vector<string>  &tokens )
	{
		stack<int> intstack;//define stack
		int i,top1=0,top2=0;
		for(i=0;i<tokens.size();i++)//traversal tokens
		{	
			// judge the value is number or operator
			if(!(tokens[i]=="+"||tokens[i]=="-"||tokens[i]=="*"||tokens[i]=="/"))
				intstack.push(atoi(tokens[i].c_str())); //if the character >0,then push it into stack
			else
				{
					//copy the top element and the next to top2 and top1,then push the two values from stack
					top2=intstack.top();
					intstack.pop();
					top1=intstack.top();
					intstack.pop();
					//caculate when meet operator
					if(tokens[i]=="+")
						intstack.push(top1+top2);
					if(tokens[i]=="-")
						intstack.push(top1-top2);
					if(tokens[i]=="*")
						intstack.push(top1*top2);
					if(tokens[i]=="/")
						intstack.push(top1/top2);
				}
		}
		return(intstack.top());
	}
};
void main()
{
	Solution ss;
	string str[]={"2","1","+","-3","*"};
	//initialize tokens ,read from str to stokens
	vector<string> tokens(str,str+sizeof(str)/sizeof(str[0]));
	cout<<ss.evalRPN(tokens)<<endl;
}