标签：blog value code val dia ati span ken opera
Evaluate the value of an arithmetic expression in Reverse Polish Notation. （Medium）
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：
根据逆波兰表达式定义，建立栈存数字
遍历字符串，遇到数字，入栈，遇到运算符，取出栈顶两元素执行相应计算后将结果入栈
代码：
1 class Solution { 2 public: 3 int evalRPN(vector<string>& tokens) { 4 stack<int> s; 5 for (int i = 0;i < tokens.size();i++) { 6 if (tokens[i] == "+" || tokens[i] == "-" || tokens[i]== "*" || tokens[i] == "/") { 7 int num1 = s.top(); 8 s.pop(); 9 int num2 = s.top(); 10 s.pop(); 11 if (tokens[i] == "+") { 12 int num = num1 + num2; 13 s.push(num); 14 } 15 if (tokens[i] == "-") { 16 int num = num2 - num1; 17 s.push(num); 18 } 19 if (tokens[i] == "*") { 20 int num = num2 * num1; 21 s.push(num); 22 } 23 if (tokens[i] == "/") { 24 int num = num2 / num1; 25 s.push(num); 26 } 27 } 28 else { 29 s.push(atoi(tokens[i].c_str())); 30 } 31 } 32 int ans = s.top(); 33 return ans; 34 } 35 };
LeetCode150 Evaluate Reverse Polish Notation
标签：blog value code val dia ati span ken opera
原文地址：http://www.cnblogs.com/wangxiaobao/p/6146708.html
