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Evaluate Reverse Polish Notation
题目描述：
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
解题方案：
该题借助一个栈，遍历tokens时，如果当前不为"+","-","*","/"，则入栈，否则将栈顶的两个元素出栈后，运算后结果入栈。下面是该题代码：
1 class Solution { 2 public: 3 int evalRPN(vector<string> &tokens) { 4 stack<int> result; 5 int a, b; 6 for (vector<string>::iterator ix = tokens.begin(); ix != tokens.end(); ++ix) { 7 if (*ix == "+" || *ix == "-" || *ix == "*" || *ix == "/") { 8 a = result.top(); 9 result.pop();10 b = result.top();11 result.pop();12 if (*ix == "+") {13 result.push(b + a);14 }15 if (*ix == "-") {16 result.push(b - a);17 }18 if (*ix == "*") {19 result.push(b * a);20 }21 if (*ix == "/") {22 result.push(b / a);23 }24 } else {25 result.push(atoi((*ix).c_str()));26 }27 }28 return result.top();29 }30 };
Evaluate Reverse Polish Notation
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