LeetCode Evaluate Reverse Polish Notation

最新推荐文章于 2019-07-18 20:00:48 发布

kassical

最新推荐文章于 2019-07-18 20:00:48 发布

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分类专栏： LeetCode 文章标签： leetcode

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本文介绍如何使用栈来解析并求值逆波兰表达式，包括加、减、乘、除运算，通过实例演示算法实现。

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> myStack;
		vector<string>::iterator iter = tokens.begin();
		for (; iter != tokens.end(); iter++) {
			if (*iter != "+" && *iter != "-" && *iter != "*" && *iter != "/") {
				int iot = atoi((*iter).c_str());
				myStack.push(iot);
			} else{
				int ia, ib;
				ib = myStack.top();
				myStack.pop();
				ia = myStack.top();
				myStack.pop();

				if (*iter == "+") {
					ia += ib;
					myStack.push(ia);
				}
				else if (*iter == "-") {
					ia -= ib;
					myStack.push(ia);
				}
				else if (*iter == "*") {
					ia *= ib;
					myStack.push(ia);
				}
				else if (*iter == "/") {
					ia /= ib;
					myStack.push(ia);
				}
			}
		}
		return myStack.top();
	}
};