【LeetCode】Evaluate Reverse Polish Notation

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

Have you been asked this question in an interview?

class Solution {
public:

    bool isoperator(string op)
    {
	    if(op == "+" || op == "-" || op == "*" || op == "/")
		    return true;
	   else return false;
    }

    int compute(int op1, int op2, string op)
        {
	    if(op == "+"){
	    	return op1+op2;
	    }
	    else if(op == "-"){
		    return op1-op2;
	    }
	    else if(op == "*"){
		    return op1*op2;
	    }
	    else return op1/op2;
	
    }

    int evalRPN(vector<string> &tokens) {
        if(tokens.size() == 1){
		return atoi(tokens[0].c_str());
	    }
        stack<string> buf;
	    for(int i = 0; i < tokens.size(); i++)
	    {
		    if(isoperator(tokens[i]))
		{
			string op1 = buf.top();
			int ope1 = atoi(op1.c_str());
			buf.pop();
			string op2 = buf.top();
			int ope2 = atoi(op2.c_str());
			buf.pop();
			int tmp = compute(ope2,ope1,tokens[i]);
			if(i == tokens.size()-1)
			{
				return tmp;
			}
			else {
				char buffer[64];
				//itoa(tmp,buffer,10);
				sprintf(buffer,"%d",tmp);
				string res(buffer);
				buf.push(res);
			}
		}
		else buf.push(tokens[i]);
	    }
    }
};

【LeetCode】Evaluate Reverse Polish Notation,布布扣,bubuko.com

【LeetCode】Evaluate Reverse Polish Notation

原文：http://blog.csdn.net/xiaozhuaixifu/article/details/21319295