leetcode 150. Evaluate Reverse Polish Notation

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于 2017-11-25 09:05:51 发布

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本文介绍了一种使用栈数据结构来解析和计算后缀表达式（逆波兰表示法）的方法。通过C++实现了一个简单的计算器，能够处理加、减、乘、除四种基本运算。

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150. 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

计算后缀表达式！用STACK

class Solution {
public:
    int evalRPN(vector<string>& tokens) 
    {
        stack<int> shuzi;
        for (int i = 0; i < tokens.size(); i++)
        {
            if(tokens[i] == "+") 
            {
                int a = shuzi.top(); 
                shuzi.pop();
                int b = shuzi.top();
                shuzi.top() = a + b; 
            } 
            else if(tokens[i] == "-") 
            {
                int a = shuzi.top(); 
                shuzi.pop();
                int b = shuzi.top();
                shuzi.top() = b - a; 
            }
            else if(tokens[i] == "*") 
            {
                int a = shuzi.top(); 
                shuzi.pop();
                int b = shuzi.top();
                shuzi.top() = a * b; 
            }
            else if(tokens[i] == "/") 
            {
                int a = shuzi.top(); 
                shuzi.pop();
                int b = shuzi.top();
                shuzi.top() = b / a; 
            }
            else
                shuzi.push( atoi(tokens[i].c_str()) );
        }
        return shuzi.top();
    }
};