LeetCode: Reverse Words in a String：Evaluate Reverse Polish Notation

LeetCode: Reverse Words in a String：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

地址：https://oj.leetcode.com/problems/evaluate-reverse-polish-notation/


计算波兰后缀表达式的值，具体做法是利用一个栈，如果遇到数字则把数字进栈，如果遇到操作符就把栈中的数字出栈进行运算（二元操作符出栈两个数字，一元操作符出栈一个数字），最后的结果存在栈中。代码：

 class Solution {

 public:

     int evalRPN(vector<string> &tokens) {

         int lop, rop;

         vector<string>::const_iterator cIter = tokens.begin();

         stack<int> s;

         for(; cIter != tokens.end(); ++cIter){

             if ((*cIter).size() ==  && !isdigit((*cIter)[])){

                 char op = (*cIter)[];

                 rop = s.top();

                 s.pop();

                 lop = s.top();

                 s.pop();

                 if ('+' == op){

                     s.push(lop + rop);

                 } else if ('-' == op){

                     s.push(lop - rop);

                 } else if ('*' == op){

                     s.push(lop * rop);

                 } else{

                     s.push(lop / rop);

                 }

             } else {

                 s.push(atoi((*cIter).c_str()));

             }

         }

         return s.top();

     }

 };

巴特西

LeetCode: Reverse Words in a String：Evaluate Reverse Polish Notation

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