【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
栈的典型应用
1 class Solution { 2 public: 3 int evalRPN(vector<string> &tokens) { 4 int ans = 0; 5 stack<int> s; 6 for(int i = 0; i < tokens.size(); ++i) { 7 if (tokens[i] == "+") { 8 int b = s.top(); 9 s.pop(); 10 int a = s.top(); 11 s.pop(); 12 a += b; 13 s.push(a); 14 } else if (tokens[i] == "-") { 15 int b = s.top(); 16 s.pop(); 17 int a = s.top(); 18 s.pop(); 19 a -= b; 20 s.push(a); 21 } else if (tokens[i] == "*") { 22 int b = s.top(); 23 s.pop(); 24 int a = s.top(); 25 s.pop(); 26 a *= b; 27 s.push(a); 28 } else if (tokens[i] == "/") { 29 int b = s.top(); 30 s.pop(); 31 int a = s.top(); 32 s.pop(); 33 a /= b; 34 s.push(a); 35 } else { 36 s.push(atoi(tokens[i].c_str())); 37 } 38 } 39 return s.top(); 40 } 41 };
