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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
分析：Reverse Polish Notation可以通过post traversal计算树来得到，我们可以通过栈来evaluate它的值，代码如下：
1 class Solution { 2 public: 3 int evalRPN(vector<string> &tokens) { 4 int result = 0; 5 stack<int> S; 6 7 for(int i = 0; i < tokens.size(); i++){ 8 if(is_operator(tokens[i])){ 9 int rv = S.top();10 S.pop();11 int lv = S.top();12 S.pop();13 if(tokens[i] == "+")14 S.push(lv + rv);15 else if(tokens[i] == "-")16 S.push(lv - rv);17 else if(tokens[i] == "*")18 S.push(lv * rv);19 else if(tokens[i] == "/")20 S.push(lv / rv);21 }else{22 S.push(atoi(tokens[i].c_str()));23 }24 }25 return S.top();26 }27 28 bool is_operator(string s){29 return s == "+" || s == "-" || s == "*" || s == "/";30 }31 };
Leetcode: Evaluate Reverse Polish Notation
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