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
使用栈(Stack)，如果是操作数则压栈，如果是操作符则弹出栈顶两个元素进行相应运算之后再压栈。
最后栈中剩余元素即计算结果。
class Solution { public: int evalRPN(vector<string> &tokens) { stack<int> stk; for(vector<string>::size_type st = 0; st < tokens.size(); st ++) { if(tokens[st] == "+") { int a = stk.top(); stk.pop(); int b = stk.top(); stk.pop(); stk.push(a+b); } else if(tokens[st] == "-") { int a = stk.top(); stk.pop(); int b = stk.top(); stk.pop(); stk.push(b-a); } else if(tokens[st] == "*") { int a = stk.top(); stk.pop(); int b = stk.top(); stk.pop(); stk.push(a*b); } else if(tokens[st] == "/") { int a = stk.top(); stk.pop(); int b = stk.top(); stk.pop(); stk.push(b/a); } else { stk.push(atoi(tokens[st].c_str())); } } return stk.top(); } };
【LeetCode】Evaluate Reverse Polish Notation
原文：http://www.cnblogs.com/ganganloveu/p/3964274.html