Leetcode 150. Evaluate Reverse Polish Notation (Medium) (cpp)

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本文介绍了一种使用栈来解决LeetCode 150题——逆波兰表达式求值的方法。该方法通过遍历输入的字符串数组，利用栈结构进行数值运算，支持加、减、乘、除四种运算。

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Leetcode 150. Evaluate Reverse Polish Notation (Medium) (cpp)

Tag: Stack

Difficulty: Medium

/*

150. Evaluate Reverse Polish Notation (Medium)

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

*/
class Solution {
public:
	int evalRPN(vector<string>& tokens) {
		stack<int> s;
		for (auto t : tokens) {
			if (t == "+" || t == "-" || t == "*" || t == "/") {
				int num2 = s.top();
				s.pop();
				int num1 = s.top();
				s.pop();
				if (t == "+") s.push(num1 + num2);
				if (t == "-") s.push(num1 - num2);
				if (t == "*") s.push(num1 * num2);
				if (t == "/") s.push(num1 / num2);
			}
			else s.push(stoi(t));
		}
		return s.top();
	}
};